U.S. patent application number 15/654124 was filed with the patent office on 2017-11-02 for ion exchange membrane for alkali chloride electrolysis, and alkali chloride electrolysis apparatus.
This patent application is currently assigned to Asahi Glass Company, Limited. The applicant listed for this patent is Asahi Glass Company, Limited. Invention is credited to Takayuki KANEKO, Hiromitsu KUSANO, Takuo NISHIO, Yasushi YAMAKI.
Application Number | 20170313836 15/654124 |
Document ID | / |
Family ID | 56848324 |
Filed Date | 2017-11-02 |
United States Patent
Application |
20170313836 |
Kind Code |
A1 |
KANEKO; Takayuki ; et
al. |
November 2, 2017 |
ION EXCHANGE MEMBRANE FOR ALKALI CHLORIDE ELECTROLYSIS, AND ALKALI
CHLORIDE ELECTROLYSIS APPARATUS
Abstract
To provide an ion exchange membrane for alkali chloride
electrolysis which has a low membrane resistance and which is
capable of reducing the electrolysis voltage during the alkali
chloride electrolysis, while increasing the membrane strength. An
ion exchange membrane 1 for alkali chloride electrolysis wherein a
reinforcing material 20 obtained by weaving with reinforcing yarns
22 and sacrificial yarns 24 is embedded in a fluoropolymer having
ion exchange groups, the ion exchange membrane 1 comprises elution
holes (28) formed by eluting at least a portion of a material of
the sacrificial yarns 24, and in a cross section perpendicular to
the length direction of the yarns, the total area (S) obtained by
adding the cross-sectional area of an elution hole 28 and the
cross-sectional area of a sacrificial yarn 24 remaining in the
elution hole 28 is from 500 to 1,200 .mu.m.sup.2, and the number
(n) of elution holes 28 between adjacent reinforcing yarns 22 is at
least 10.
Inventors: |
KANEKO; Takayuki;
(Chiyoda-ku, JP) ; KUSANO; Hiromitsu; (Chiyoda-ku,
JP) ; YAMAKI; Yasushi; (Chiyoda-ku, JP) ;
NISHIO; Takuo; (Chiyoda-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Asahi Glass Company, Limited |
Chiyoda-ku |
|
JP |
|
|
Assignee: |
Asahi Glass Company,
Limited
Chiyoda-ku
JP
|
Family ID: |
56848324 |
Appl. No.: |
15/654124 |
Filed: |
July 19, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2016/056488 |
Mar 2, 2016 |
|
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15654124 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08J 5/2237 20130101;
C25B 1/46 20130101; C25B 13/02 20130101; C25B 13/08 20130101; C01B
7/03 20130101; B01J 47/12 20130101; C08J 5/2281 20130101; C25B 9/00
20130101; C08J 2427/18 20130101; B01J 39/20 20130101 |
International
Class: |
C08J 5/22 20060101
C08J005/22; B01J 47/12 20060101 B01J047/12; B01J 39/20 20060101
B01J039/20; C08J 5/22 20060101 C08J005/22; C25B 13/08 20060101
C25B013/08; C25B 1/46 20060101 C25B001/46 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 2015 |
JP |
2015-041301 |
Claims
1. An ion exchange membrane for alkali chloride electrolysis
comprising a fluoropolymer having ion exchange groups, a
reinforcing material embedded in the fluoropolymer and formed of
reinforcing yarns and optionally contained sacrificial yarns, and
elution holes of the sacrificial yarns present between the
reinforcing yarns, characterized in that in a cross section
perpendicular to the length direction of the reinforcing yarns
forming the reinforcing material, the total area (S) obtained by
adding the cross-sectional area of an elution hole and the
cross-sectional area of a sacrificial yarn remaining in the elution
hole is from 500 to 1,200 .mu.m.sup.2, and the number (n) of
elution holes between adjacent reinforcing yarns is at least
10.
2. The ion exchange membrane for alkali chloride electrolysis
according to claim 1, wherein in a cross section perpendicular to
the length direction of the reinforcing yarns forming the
reinforcing material, the average distance (d1) from the center of
a reinforcing yarn to the center of the adjacent reinforcing yarn
is from 750 to 1,500 .mu.m.
3. The ion exchange membrane for alkali chloride electrolysis
according to claim 1, wherein a relationship is established to
satisfy the following formula (1) in a cross section perpendicular
to the length direction of the reinforcing yarns:
0.5.ltoreq.{d2/d1.times.(n+1)}.ltoreq.1.5 (1) provided that the
symbols in the formula (1) have the following meanings, d1: the
average distance from the center of a reinforcing yarn to the
center of the adjacent reinforcing yarn, d2: the average distance
from the center of an elution hole to the center of the adjacent
elution hole, n: the number of elution holes between adjacent
reinforcing yarns.
4. The ion exchange membrane for alkali chloride electrolysis
according to claim 3, wherein a relationship is established to
satisfy the following formula (1') at all measurement points
measured to determine the average distance (d1) and the average
distance (d2) in a cross section perpendicular to the length
direction of the reinforcing yarns:
0.5.ltoreq.{d2'/d1.times.(n+1)}.ltoreq.1.5 (1') provided that the
symbols in the formula (1') have the following meanings, d2': the
distance from the center of an elution hole to the center of the
adjacent elution hole, d1 and n: the same as above.
5. The ion exchange membrane for alkali chloride electrolysis
according to claim 1, wherein a relationship is established to
satisfy the following formula (2) in a cross section perpendicular
to the length direction of the reinforcing yarns:
1.0.ltoreq.{d3/d1.times.(n+1)}.ltoreq.2.0 (2) provided that the
symbols in the formula (2) have the following meanings, d3: the
average distance from the center of a reinforcing yarn to the
center of the adjacent elution hole, d1 and n: the same as
above.
6. The ion exchange membrane for alkali chloride electrolysis
according to claim 5, wherein a relationship is established to
satisfy the following formula (2') at all measurement points
measured to determine the average distance (d1) and the average
distance (d3) in a cross section perpendicular to the length
direction of the reinforcing yarns:
1.0.ltoreq.{d3'/d1.times.(n+1)}.ltoreq.2.0 (2') provided that the
symbols in the formula (2') have the following meanings, d3': the
distance from the center of an elution hole to the center of the
adjacent elution hole, d1 and n: the same as above.
7. The ion exchange membrane for alkali chloride electrolysis
according to claim 1, wherein the widths of said reinforcing yarns
in a cross section perpendicular to the length direction of the
reinforcing yarns are from 70 to 160 .mu.m.
8. The ion exchange membrane for alkali chloride electrolysis
according to claim 1, wherein the fluoropolymer having ion exchange
groups includes a fluoropolymer having carboxylic acid functional
groups and a fluoropolymer having sulfonic acid functional groups,
and the reinforcing material is embedded in the fluoropolymer
having sulfonic acid functional groups.
9. An alkali chloride electrolysis apparatus comprising an
electrolytic cell provided with a cathode and an anode, and an ion
exchange membrane for alkali chloride electrolysis as defined in
claim 1 partitioning a cathode chamber on the cathode side and an
anode chamber on the anode side in the electrolytic cell.
10. A method for producing an ion exchange membrane for alkali
chloride electrolysis, which comprises obtaining a reinforcing
precursor membrane having a reinforcing fabric composed of
reinforcing yarns and sacrificial yarns, embedded in a precursor
membrane comprising a fluoropolymer having groups convertible to
ion exchange groups, and then contacting the reinforcing precursor
membrane to an alkaline aqueous solution to convert the groups
convertible to ion exchange groups, to ion exchange groups, and at
the same time to elute at least a portion of the sacrificial yarns
in the reinforcing fabric, thereby to obtain an ion exchange
membrane comprising a fluoropolymer having ion exchange groups, a
reinforcing material having at least a portion of the sacrificial
yarns in the reinforcing fabric eluted, and elution holes,
characterized in that in a cross section perpendicular to the
length direction of the reinforcing yarns forming the reinforcing
material in the ion exchange membrane, the total area (S) obtained
by adding the cross-sectional area of an elution hole and the
cross-sectional area of a sacrificial yarn remaining in the elution
hole, is from 500 to 1,200 .mu.m.sup.2, and the number (n) of
elution holes between adjacent reinforcing yarns is at least
10.
11. The method for producing an ion exchange membrane for alkali
chloride electrolysis according to claim 10, wherein in a cross
section perpendicular to the length direction of the reinforcing
yarns forming the reinforcing material, the average distance (d1)
from the center of a reinforcing yarn to the center of the adjacent
reinforcing yarn is from 750 to 1,500 .mu.m.
12. The method for producing an ion exchange membrane for alkali
chloride electrolysis according to claim 10, wherein a relationship
is established to satisfy the following formula (1) in a cross
section perpendicular to the length direction of the reinforcing
yarns: 0.5.ltoreq.{d2/d1.times.(n+1)}.ltoreq.1.5 (1) provided that
the symbols in the formula (1) have the following meanings, d1: the
average distance from the center of a reinforcing yarn to the
center of the adjacent reinforcing yarn, d2: the average distance
from the center of an elution hole to the center of the adjacent
elution hole, n: the number of elution holes between adjacent
reinforcing yarns.
13. The method for producing an ion exchange membrane for alkali
chloride electrolysis according to claim 12, wherein a relationship
is established to satisfy the following formula (1') at all
measurement points measured to determine the average distance (d2)
in a cross section perpendicular to the length direction of the
reinforcing yarns: 0.5.ltoreq.{d2'/d1.times.(n+1)}.ltoreq.1.5 (1')
provided that the symbols in the formula (1') have the following
meanings, d2': the distance from the center of an elution hole to
the center of the adjacent elution hole, d1 and n: the same as
above.
14. The method for producing an ion exchange membrane for alkali
chloride electrolysis according to claim 10, wherein a relationship
is established to satisfy the following formula (2) in a cross
section perpendicular to the length direction of the reinforcing
yarns: 1.0.ltoreq.{d3/d1.times.(n+1)}.ltoreq.2.0 (2) provided that
the symbols in the formula (2) have the following meanings, d3: the
average distance from the center of a reinforcing yarn to the
center of the adjacent elution hole or sacrificial yarn, d1 and n:
the same as above.
15. The method for producing an ion exchange membrane for alkali
chloride electrolysis according to claim 14, wherein a relationship
is established to satisfy the following formula (2') at all
measurement points measured to determine the average distance (d3)
in a cross section perpendicular to the length direction of the
reinforcing yarns: 1.0.ltoreq.{d3'/d1.times.(n+1)}.ltoreq.2.0 (2')
provided that the symbols in the formula (2') have the following
meanings, d3': the distance from the center of a reinforcing yarn
to the center of the adjacent elution hole, d1 and n: the same as
above.
16. The method for producing an ion exchange membrane for alkali
chloride electrolysis according to claim 10, wherein the widths of
said reinforcing yarns in a cross section perpendicular to the
length direction of the reinforcing yarns are from 70 to 160
.mu.m.
17. A method for producing an alkaline chloride electrolysis
apparatus, characterized by obtaining an ion exchange membrane for
alkali chloride electrolysis by the method as defined in claim 10,
and then disposing the ion exchange membrane as an electrolyte
membrane partitioning a cathode chamber on the cathode side and an
anode chamber on the anode side in the electrolytic cell.
Description
TECHNICAL FIELD
[0001] The present invention relates to an ion exchange membrane
for alkali chloride electrolysis, and an alkali chloride
electrolysis apparatus.
BACKGROUND ART
[0002] As an ion exchange membrane to be used in an alkali chloride
electrolysis method for producing an alkali hydroxide and chlorine
by electrolyzing an alkali chloride aqueous solution such as
seawater, an electrolyte membrane made of a fluoropolymer having
ion-exchange groups (carboxylic acid functional groups, sulfonic
acid functional groups, etc.) is known.
[0003] In order to maintain the mechanical strength and dimensional
stability, the electrolyte membrane is usually reinforced by a
reinforcing fabric made of reinforcing yarns (such as
polytetrafluoroethylene (hereinafter referred to as PTFE.) yarns).
However, with an ion-exchange membrane having a reinforcing fabric
made of PTFE yarns, etc., the membrane resistance tends to be high,
and the electrolysis voltage tends to increase.
[0004] Therefore, a method using a reinforcing fabric obtained by
interweaving reinforcing yarns of PTFE, etc. and sacrificial yarns
soluble in an alkaline aqueous solution, such as polyethylene
terephthalate (hereinafter referred to as PET) yarns, has been
proposed (e.g. Patent Document 1).
PRIOR ART DOCUMENT
Patent Document
[0005] Patent Document 1: JP-A-2004-43594
DISCLOSURE OF INVENTION
Technical Problem
[0006] In the ion exchange membrane using the above-mentioned
reinforcing fabric comprising the reinforcing yarns and the
sacrificial yarns, in order to enhance the membrane strength, it is
important to further narrow the spacing between reinforcing yarns
in the reinforcing fabric. However, if the spacing between
reinforcing yarns is narrowed, the membrane resistance will
increase, and the electrolysis voltage becomes high. Therefore, it
is difficult to reduce the electrolysis voltage, while increasing
the membrane strength of the ion exchange membrane.
[0007] It is an object of the present invention to provide an ion
exchange membrane for alkali chloride electrolysis which has a low
membrane resistance and which is capable of reducing the
electrolysis voltage during the alkali chloride electrolysis, even
if the spacing between reinforcing yarns is made narrow to increase
the membrane strength, and an alkali chloride electrolysis
apparatus using such an ion exchange membrane for alkali chloride
electrolysis.
Solution to Problem
[0008] The present invention has the following constructions.
[1] An ion exchange membrane for alkali chloride electrolysis
comprising a fluoropolymer having ion exchange groups, a
reinforcing material embedded in the fluoropolymer and formed of
reinforcing yarns and optionally contained sacrificial yarns, and
elution holes of the sacrificial yarns present between the
reinforcing yarns, characterized in that
[0009] in a cross section perpendicular to the length direction of
the reinforcing yarns forming the reinforcing material, the total
area (S) obtained by adding the cross-sectional area of an elution
hole and the cross-sectional area of a sacrificial yarn remaining
in the elution hole is from 500 to 1,200 .mu.m.sup.2, and
[0010] the number (n) of elution holes between adjacent reinforcing
yarns is at least 10.
[2] The ion exchange membrane for alkali chloride electrolysis
according to the above [1], wherein in a cross section
perpendicular to the length direction of the reinforcing yarns
forming the reinforcing material, the average distance (d1) from
the center of a reinforcing yarn to the center of the adjacent
reinforcing yarn is from 750 to 1,500 .mu.m. [3] The ion exchange
membrane for alkali chloride electrolysis according to the above
[1] or [2], wherein a relationship is established to satisfy the
following formula (1) in a cross section perpendicular to the
length direction of the reinforcing yarns:
0.5.ltoreq.{d2/d1.times.(n+1)}.ltoreq.1.5 (1)
provided that the symbols in the formula (1) have the following
meanings,
[0011] d1: the average distance from the center of a reinforcing
yarn to the center of the adjacent reinforcing yarn,
[0012] d2: the average distance from the center of an elution hole
to the center of the adjacent elution hole,
[0013] n: the number of elution holes between adjacent reinforcing
yarns.
[4] The ion exchange membrane for alkali chloride electrolysis
according to the above [3], wherein a relationship is established
to satisfy the following formula (1') at all measurement points
measured to determine the average distance (d1) and the average
distance (d2) in a cross section perpendicular to the length
direction of the reinforcing yarns:
0.5.ltoreq.{d2'/d1.times.(n+1)}.ltoreq.1.5 (1')
provided that the symbols in the formula (1') have the following
meanings,
[0014] d2': the distance from the center of an elution hole to the
center of the adjacent elution hole,
[0015] d1 and n: the same as above.
[5] The ion exchange membrane for alkali chloride electrolysis
according to any one of the above [1] to [4], wherein a
relationship is established to satisfy the following formula (2) in
a cross section perpendicular to the length direction of the
reinforcing yarns:
1.0.ltoreq.{d3/d1.times.(n+1)}.ltoreq.2.0 (2)
provided that the symbols in the formula (2) have the following
meanings,
[0016] d3: the average distance from the center of a reinforcing
yarn to the center of the adjacent elution hole,
[0017] d1 and n: the same as above.
[6] The ion exchange membrane for alkali chloride electrolysis
according to the above [5], wherein a relationship is established
to satisfy the following formula (2') at all measurement points
measured to determine the average distance (d1) and the average
distance (d3) in a cross section perpendicular to the length
direction of the reinforcing yarns:
1.0.ltoreq.{d3'/d1.times.(n+1)}.ltoreq.2.0 (2')
provided that the symbols in the formula (2') have the following
meanings,
[0018] d3': the distance from the center of an elution hole to the
center of the adjacent elution hole,
[0019] d1 and n: the same as above.
[7] The ion exchange membrane for alkali chloride electrolysis
according to any one of the above [1] to [6], wherein the widths of
said reinforcing yarns in a cross section perpendicular to the
length direction of the reinforcing yarns are from 70 to 160 .mu.m.
[8] The ion exchange membrane for alkali chloride electrolysis
according to any one of the above [1] to [7], wherein the
fluoropolymer having ion exchange groups includes a fluoropolymer
having carboxylic acid functional groups and a fluoropolymer having
sulfonic acid functional groups, and the reinforcing material is
embedded in the fluoropolymer having sulfonic acid functional
groups. [9] An alkali chloride electrolysis apparatus comprising an
electrolytic cell provided with a cathode and an anode, and an ion
exchange membrane for alkali chloride electrolysis as defined in
any one of the above [1] to [7] partitioning a cathode chamber on
the cathode side and an anode chamber on the anode side in the
electrolytic cell. [10] A method for producing an ion exchange
membrane for alkali chloride electrolysis, which comprises
obtaining a reinforcing precursor membrane having a reinforcing
fabric composed of reinforcing yarns and sacrificial yarns,
embedded in a precursor membrane comprising a fluoropolymer having
groups convertible to ion exchange groups, and then contacting the
reinforcing precursor membrane to an alkaline aqueous solution to
convert the groups convertible to ion exchange groups, to ion
exchange groups, and at the same time to elute at least a portion
of the sacrificial yarns in the reinforcing fabric, thereby to
obtain an ion exchange membrane comprising a fluoropolymer having
ion exchange groups, a reinforcing material having at least a
portion of the sacrificial yarns in the reinforcing fabric eluted,
and elution holes, characterized in that
[0020] in a cross section perpendicular to the length direction of
the reinforcing yarns forming the reinforcing material in the ion
exchange membrane,
[0021] the total area (S) obtained by adding the cross-sectional
area of an elution hole and the cross-sectional area of a
sacrificial yarn remaining in the elution hole, is from 500 to
1,200 .mu.m.sup.2, and
[0022] the number (n) of elution holes between adjacent reinforcing
yarns is at least 10.
[11] The method for producing an ion exchange membrane for alkali
chloride electrolysis according to the above [10], wherein in a
cross section perpendicular to the length direction of the
reinforcing yarns forming the reinforcing material, the average
distance (d1) from the center of a reinforcing yarn to the center
of the adjacent reinforcing yarn is from 750 to 1,500 .mu.m. [12]
The method for producing an ion exchange membrane for alkali
chloride electrolysis according to the above [10] or [11], wherein
a relationship is established to satisfy the following formula (1)
in a cross section perpendicular to the length direction of the
reinforcing yarns:
0.5.ltoreq.{d2/d1.times.(n+1)}.ltoreq.1.5 (1)
provided that the symbols in the formula (1) have the following
meanings,
[0023] d1: the average distance from the center of a reinforcing
yarn to the center of the adjacent reinforcing yarn,
[0024] d2: the average distance from the center of an elution hole
to the center of the adjacent elution hole,
[0025] n: the number of elution holes between adjacent reinforcing
yarns.
[13] The method for producing an ion exchange membrane for alkali
chloride electrolysis according to the above [11], wherein a
relationship is established to satisfy the following formula (1')
at all measurement points measured to determine the average
distance (d2) in a cross section perpendicular to the length
direction of the reinforcing yarns:
0.5.ltoreq.{d2'/d1.times.(n+1)}.ltoreq.1.5 (1')
provided that the symbols in the formula (1') have the following
meanings,
[0026] d2': the distance from the center of an elution hole to the
center of the adjacent elution hole,
[0027] d1 and n: the same as above.
[14] The method for producing an ion exchange membrane for alkali
chloride electrolysis according to any one of the above [10] to
[12], wherein a relationship is established to satisfy the
following formula (2) in a cross section perpendicular to the
length direction of the reinforcing yarns:
1.0.ltoreq.{d3/d1.times.(n+1)}.ltoreq.2.0 (2)
provided that the symbols in the formula (2) have the following
meanings,
[0028] d3: the average distance from the center of a reinforcing
yarn to the center of the adjacent elution hole or sacrificial
yarn,
[0029] d1 and n: the same as above.
[15] The method for producing an ion exchange membrane for alkali
chloride electrolysis according to the above [14], wherein a
relationship is established to satisfy the following formula (2')
at all measurement points measured to determine the average
distance (d3) in a cross section perpendicular to the length
direction of the reinforcing yarns:
1.0.ltoreq.{d3'/d1.times.(n+1)}.ltoreq.2.0 (2')
provided that the symbols in the formula (2') have the following
meanings,
[0030] d3': the distance from the center of a reinforcing yarn to
the center of the adjacent elution hole,
[0031] d1 and n: the same as above.
[16] The method for producing an ion exchange membrane for alkali
chloride electrolysis according to any one of the above [10] to
[15], wherein the widths of said reinforcing yarns in a cross
section perpendicular to the length direction of the reinforcing
yarns are from 70 to 160 .mu.m. [17] A method for producing an
alkaline chloride electrolysis apparatus, characterized by
obtaining an ion exchange membrane for alkali chloride electrolysis
by the method as defined in any one of the above [10] to [16], and
then disposing the ion exchange membrane as an electrolyte membrane
partitioning a cathode chamber on the cathode side and an anode
chamber on the anode side in the electrolytic cell.
Advantageous Effects of Invention
[0032] The ion exchange membrane for alkali chloride electrolysis
of the present invention has low membrane resistance and is capable
of reducing the electrolysis voltage during the alkaline chloride
electrolysis even if the spacing between reinforcing yarns is made
narrow to increase the membrane strength.
[0033] The alkali chloride electrolysis apparatus of the present
invention has an ion-exchange membrane for alkali chloride
electrolysis having a high membrane strength, and the membrane
resistance is low, and the electrolysis voltage at the time of
alkali chloride electrolysis is low.
BRIEF DESCRIPTION OF DRAWINGS
[0034] FIG. 1 is a schematic cross-sectional view showing one
example of the ion exchange membrane for alkali chloride
electrolysis of the present invention.
[0035] FIG. 2 is a schematic enlarged cross-sectional view of the
vicinity of the surface of the layer (S) in the ion exchange
membrane of alkali chloride electrolysis in FIG. 1.
[0036] FIG. 3 is a schematic diagram showing an example of the
alkali chloride electrolysis apparatus of the present
invention.
DESCRIPTION OF EMBODIMENTS
[0037] The following definitions of terms apply throughout the
present specification including claims.
[0038] An "ion exchange group" is a group wherein at least a
portion of ions contained therein may be exchanged for another
ion.
[0039] A "carboxylic acid functional group" means a carboxylic acid
group (--COOH) or --COOM.sup.1 (wherein M.sup.1 is an alkali metal
or a quaternary ammonium base).
[0040] A "sulfonic acid functional group" means a sulfonic acid
group (--SO.sub.3H) or --SO.sub.3M.sup.2 (wherein M.sup.2 is an
alkali metal or a quaternary ammonium base).
[0041] A "group convertible to an ion exchange group" means a group
which can be converted to an ion exchange group by a known
treatment such as hydrolysis treatment, acid form treatment,
etc.
[0042] A "group convertible to a carboxylic acid functional group"
is a group which can be converted to a carboxylic acid functional
group by a known treatment such as hydrolysis treatment, acid form
treatment, etc.
[0043] A "group convertible to a sulfonic acid functional group" is
a group which can be converted to a sulfonic acid functional group
by a known treatment such as hydrolysis treatment, acid form
treatment, etc.
[0044] A "fluoropolymer" means a polymer compound having fluorine
atom(s) in the molecule.
[0045] A "perfluorocarbon polymer" means a polymer wherein all of
hydrogen atoms bonded to carbon atoms in the polymer are
substituted by fluorine atoms. Some of the fluorine atoms in the
perfluorocarbon polymer may be substituted by chlorine atom(s) or
bromine atom(s).
[0046] A "monomer" means a compound having a polymerization
reactive carbon-carbon double bond.
[0047] A "fluoromonomer" means a monomer having fluorine atom(s) in
the molecule.
[0048] A "unit" means a moiety derived from a monomer present in a
polymer to constitute the polymer. A unit derived from a monomer,
which is formed by addition polymerization of the monomer having a
carbon-carbon unsaturated double bond, is a divalent unit formed by
cleavage of the unsaturated double bond. Further, one having the
structure of a certain unit chemically converted after polymer
formation may also be referred to as a unit. In the following, in
some cases, units derived from an individual monomer may be
represented by a name having the monomer's name followed by
"units".
[0049] A "reinforcing fabric" means a fabric which is used as a raw
material for a reinforcing material to improve the strength of an
ion exchange membrane. In the present specification, the
"reinforcing fabric" is formed by weaving reinforcing yarns and
sacrificial yarns. Reinforcing yarns and sacrificial yarns of the
reinforcing fabric are woven as warps and wefts, respectively, and
these warps and wefts are orthogonal in the case of a usual weaving
method such as plain weaving.
[0050] A "reinforcing material" is a material which is used to
improve the strength of an ion exchange membrane, and means a
material formed of reinforcing yarns and optionally contained
sacrificial yarns derived from the reinforcing fabric, which is
formed in the process for producing an ion exchange membrane, by
immersing a reinforcing precursor membrane made of a fluoropolymer
having a reinforcing fabric embedded therein, in an alkaline
aqueous solution (such as sodium hydroxide aqueous solution and
potassium hydroxide aqueous solution), so that at least a portion
of the sacrificial yarns of the reinforcing fabric is eluted. When
a portion of the sacrificial yarns is dissolved, the reinforcing
material will be composed of the reinforcing yarns and dissolution
residues of the sacrificial yarns, and when all of the sacrificial
yarns are dissolved, the reinforcing yarns will be composed solely
of the reinforcing yarns. That is, the reinforcing material is a
material formed of reinforcing yarns and optionally contained
sacrificial yarns. The reinforcing material is embedded in an ion
exchange membrane, and will be formed by immersing a reinforcing
precursor membrane made of a fluoropolymer having a reinforcing
fabric embedded therein, in an alkaline aqueous solution.
[0051] Reinforcing yarns constituting the reinforcing material are
derived from a reinforcing fabric and are thus comprised of warps
and wefts. These warps and wefts are usually orthogonal and are,
respectively, present in parallel to the MD direction and the TD
direction of the ion exchange membrane.
[0052] Here, the MD (Machine Direction) is a direction in which, in
the production of an ion exchange membrane, a precursor membrane, a
reinforcing precursor membrane and an ion exchange membrane are
conveyed. The TD (Transverse Direction) is a direction
perpendicular to the MD direction.
[0053] A "sacrificial yarn" is a yarn constituting a reinforcing
fabric and means a yarn made of a material which will elute in a
sodium hydroxide aqueous solution (e.g. an aqueous solution with a
concentration of 32 mass %), when the reinforcing fabric is
immersed therein. One sacrificial yarn may be a monofilament
consisting of one filament or may be a multifilament composed of
two or more filaments. In a case where a sacrificial yarn is a
multifilament, an assembly of two or more filaments constitutes one
sacrificial yarn. A sacrificial yarn will form an elution hole, as
at least a portion thereof is eluted when a reinforcing precursor
membrane made of a fluoropolymer having a reinforcing fabric
embedded therein is immersed in an alkaline aqueous solution such
as sodium hydroxide aqueous solution and potassium hydroxide
aqueous solution. When a portion of a sacrificial yarn is eluted,
the rest of the sacrificial yarn will remain undissolved in the
elution hole. As the alkaline aqueous solution, for example, a
sodium hydroxide aqueous solution with a concentration of 32 mass
%, may be mentioned.
[0054] An "elution hole" means a hole to be formed as a result of
elution of one sacrificial yarn when the yarn is immersed in a
sodium hydroxide aqueous solution (e.g. an aqueous solution with a
concentration of 32 mass %). In a case where the one sacrificial
yarn is a monofilament, at least a portion of the material of the
monofilament will be eluted, whereby one hole will be formed in the
ion exchange membrane. In a case where one sacrificial yarn is a
multifilament, at least a portion of the multifilament will be
eluted, whereby a collection of plural holes will be formed in the
ion exchange membrane, and this collection of plural holes is one
elution hole.
[0055] A "reinforcing yarn" is a yarn constituting a reinforcing
fabric and means a yarn made of a material which will not be eluted
even if immersed in a sodium hydroxide aqueous solution (e.g. an
aqueous solution with a concentration of 32 mass %). Even after
immersing a reinforcing precursor membrane made of a fluoropolymer
having a reinforcing fabric embedded therein, in an alkaline
aqueous solution, whereby the sacrificial yarns are eluted from the
reinforcing fabric, it remains undissolved as a yarn constituting
the reinforcing material and maintains the mechanical strength and
dimensional stability of the ion exchange membrane for alkali
chloride electrolysis.
[0056] A "center of a reinforcing yarn" means the center in the
width direction of a reinforcing yarn in a cross section
perpendicular to the length direction of the reinforcing yarns of
an ion exchange membrane.
[0057] A "center of an elution hole" means the center in the width
direction of an elution hole in a cross section perpendicular to
the length direction of the reinforcing yarns of an ion exchange
membrane. In a case where a sacrificial yarn is a monofilament, the
center of the sacrificial yarn before elution and the center of the
elution hole will coincide with each other. In a case where the
sacrificial yarn is a multifilament, the center of an elution hole
is meant for an intermediate point, in the above-mentioned cross
section, between the one end of holes and the other end of holes in
the width direction.
[0058] An "aperture ratio" means a ratio of the area of the portion
excluding the reinforcing yarns, to the area in the surface
direction of the reinforcing material.
[0059] A "reinforcing precursor membrane" means a membrane having a
reinforcing fabric composed of reinforcing yarns and sacrificial
yarns embedded in a precursor membrane comprising a fluoropolymer
having groups convertible to ion exchange groups. It is preferred
that two precursor membranes comprising a fluoropolymer having
groups convertible to ion exchange groups, are prepared, and a
reinforcing fabric is laminated between the two precursor
membranes.
[0060] A "precursor membrane" means a membrane comprising a
fluoropolymer having groups convertible to ion exchange groups. It
may be a membrane composed of a single layer of a fluoropolymer
having groups convertible to ion exchange groups, or it may be a
membrane composed of a plurality of such layers.
[0061] Hereinafter, an ion exchange membrane of the present
invention will be described with reference to FIG. 1, but the
present invention is not limited to the contents of FIG. 1.
<Ion Exchange Membrane for Alkali Chloride Electrolysis>
[0062] The ion exchange membrane for alkali chloride electrolysis
of the present invention comprises a fluoropolymer having ion
exchange groups, a reinforcing material formed of reinforcing yarns
and optionally contained sacrificial yarns, present in a state of
being embedded in said fluoropolymer, and elution holes formed by
elution of said sacrificial yarns present between said reinforcing
yarns.
[0063] FIG. 1 is a schematic cross-sectional view showing one
example of the ion exchange membrane for alkali chloride
electrolysis of the present invention.
[0064] The ion exchange membrane 1 for alkali chloride electrolysis
(hereinafter referred to as "ion exchange membrane 1") is one
having an electrolyte membrane 10 comprising a fluoropolymer having
ion exchange groups, reinforced by a reinforcing fabric 20.
[Electrolyte Membrane]
[0065] The electrolyte membrane 10 is a laminate comprising a layer
12 made of a fluoropolymer having carboxylic acid functional
groups, as a functional layer exhibiting high current efficiency,
and a layer 14a and layer 14b made of a fluoropolymer having
sulfonic acid functional groups, to maintain the mechanical
strength.
(Layer 12 Made of Fluoropolymer Having Carboxylic Acid Functional
Groups)
[0066] As the layer 12 (hereinafter referred to also as "layer
(C)") made of a fluoropolymer having carboxylic acid functional
groups (hereinafter referred to also as "fluoropolymer (C)"), for
example, a copolymer comprising units derived from a fluoromonomer
having a carboxylic acid functional group and units derived from a
fluoro-olefin, may be mentioned.
[0067] The fluoropolymer (C) is obtained by converting groups
convertible to carboxylic acid functional groups in a fluoropolymer
having the groups convertible to carboxylic acid functional groups
as described later (hereinafter referred to also as "fluoropolymer
(C')") in a step (b) described below, to carboxylic acid functional
groups.
[0068] The layer (C) usually has a membrane form. The thickness of
the layer (C) is preferably from 5 to 50 .mu.m, more preferably
from 10 to 35 .mu.m. When the thickness of the layer (C) is at
least the above lower limit value, a high current efficiency is
likely to be expressed. Further, in a case where electrolysis of
sodium chloride is conducted, it is possible to reduce the amount
of sodium chloride in sodium hydroxide as the product. When the
thickness of the layer (C) is at most the above upper limit value,
the membrane resistance of the ion exchange membrane 1 is
suppressed to be low, and the electrolysis voltage is likely to be
low.
(Layer 14a and Layer 14b Made of Fluoropolymer Having Sulfonic Acid
Functional Groups)
[0069] As a layer 14a (hereinafter referred to also as "layer
(Sa)") and a layer 14b (hereinafter referred to also as "layer
(Sb)") made of a fluoropolymer having sulfonic acid functional
groups (hereinafter referred to also as "fluoropolymer (S)"), a
copolymer comprising units derived from a fluoromonomer having a
sulfonic acid functional group and units derived from a
fluoro-olefin, may be mentioned.
[0070] The fluoropolymer (S) is obtained by converting, in a step
(b) as described below, groups convertible to sulfonic acid groups
in a fluoropolymer having the groups convertible to sulfonic acid
functional groups as described later (hereinafter referred to also
as "fluoropolymer (S')", to sulfonic acid functional groups.
[0071] FIG. 1 shows a state wherein a reinforcing material 20 is
embedded between the layer (Sa) and the layer (Sb) (hereinafter the
layer (Sa) and layer (Sb) will be collectively referred to also as
"layer (S)"). In a laminated structure of two layers (Sa) and (Sb),
the reinforcing material 20 is embedded between the two layers and
as a result, is embedded in the layer (S).
[0072] In FIG. 1, the layer (Sa) and the layer (Sb) are each a
single layer, but each of them may be formed of plural layers.
[0073] The thickness of the layer (Sb) is preferably from 30 to 140
.mu.m, more preferably from 30 to 100 .mu.m. When the thickness of
the layer (Sb) is at least the lower limit value, the mechanical
strength of the ion exchange membrane 1 will be sufficiently high.
When the thickness of the layer (Sb) is at most the upper limit
value, membrane resistance of the ion exchange membrane 1 will be
suppressed to be sufficiently low, and increase of the electrolysis
voltage will be sufficiently suppressed.
[0074] The thickness of the layer (Sa) is preferably from 10 to 60
.mu.m, more preferably from 10 to 40 .mu.m. When the thickness of
the layer (Sa) is at least the lower limit value, the reinforcing
fabric 20 fits into the electrolyte membrane 10 thereby to improve
peeling resistance of the reinforcing fabric 20. Further, the
reinforcing fabric 20 will not be too close to the surface of the
electrolyte membrane 10, whereby cracking is less likely to enter
the surface of the electrolyte membrane 10, and as a result,
lowering of the mechanical strength can be prevented. When the
thickness of the layer (Sa) is at most the upper limit value, the
membrane resistance of the ion exchange membrane 1 will be
suppressed to be sufficiently low, and increase of the electrolysis
voltage will be sufficiently suppressed.
(Reinforcing Material)
[0075] The reinforcing material 20 is a reinforcing material for
reinforcing the electrolyte membrane 10, and is a textile using a
reinforcing fabric as a starting material and obtained by weaving
with reinforcing yarns 22 and sacrificial yarns 24.
[0076] In the ion exchange membrane of the present invention, in
order to secure the effect of the present invention, it is
important that in a cross section perpendicular to the length
direction of the reinforcing yarns forming the reinforcing
material, the number of elution holes, and the total area of the
sum of the cross-sectional area of an elution hole and the
cross-sectional area of a sacrificial yarn remaining undissolved in
the elution hole, are in specific ranges.
[0077] That is, in the ion exchange membrane of the present
invention, in a cross section perpendicular to the length direction
of the reinforcing yarns of the ion exchange membrane 1, the
average distance (d1) from the center of a reinforcing yarn 22 to
the center of the adjacent reinforcing yarn 22 is from 750 to 1,500
.mu.m, preferably from 750 to 1,300 .mu.m, preferably from 800 to
1,200 .mu.m, more preferably from 800 to 1,100 .mu.m, particularly
preferably from 800 to 1,000 .mu.m, more particularly preferably
from 900 to 1,000 .mu.m. When the average distance (d1) is within
this range, it is possible to reduce the electrolysis voltage
during alkali chloride electrolysis, while increasing the membrane
strength. When the average distance (d1) is at least the lower
limit value, it is easy to reduce the electrolysis voltage during
alkali chloride electrolysis. When the average distance (d1) is at
most the upper limit value, it is easy to increase the membrane
strength of the ion exchange membrane 1.
[0078] The average distance (d1) means an average value of measured
values of the distance from the center of a reinforcing yarn to the
center of the adjacent reinforcing yarn in each of the MD cross
section perpendicular to the length direction of the reinforcing
yarns of the ion exchange membrane (cross section cut perpendicular
to the MD direction) perpendicular to the length direction of the
warps of the reinforcing yarns and the TD cross section (cross
section cut perpendicular to the TD direction). The average value
in the present invention is an average value of the measured values
of distances measured at 10 points randomly selected in each cross
section, and the same applies to values other than d1.
[0079] In the present invention, it is preferred that the
above-mentioned distance from the center of a reinforcing yarn to
the center of the adjacent reinforcing yarn in a cross section
perpendicular to the length direction of the reinforcing yarns of
the ion exchange membrane, is within the above range at all the
measurement points. It becomes thereby easy to obtain the effect to
reduce the electrolysis voltage during the alkali chloride
electrolysis, while increasing the membrane strength. All
measurement points are meant for all points measured at random in
order to calculate the average value. The same applies to values
other than d1.
[0080] The density (the number of implantation) of reinforcing
yarns 22 in the reinforcing fabric 20 is preferably from 15 to 34
yarns/inch, more preferably from 18 to 34 yarns/inch, particularly
preferably from 20 to 34 yarns/inch, more particularly preferably
20 to 30 yarns/inch, most particularly preferably 24 to 30
yarns/inch. When the density of the reinforcing yarns 22 is at
least the above lower limit value, the mechanical strength as a
reinforcing material will be sufficiently high. When the density of
the reinforcing yarns 22 is at most the upper limit value, the
membrane resistance of the ion exchange membrane 1 can be
suppressed to be sufficiently low, and increase of the electrolysis
voltage can be sufficiently suppressed.
[0081] The density of sacrificial yarns 24 in the reinforcing
fabric in order to form the reinforcing material is preferably an
even multiple of the density of the reinforcing yarns 22.
Specifically, the density of sacrificial yarns 24 is preferably 10
times or 12 times the density of the reinforcing yarns 22. When it
is an odd multiple, the warp and weft reinforcing yarns 22 do not
cross vertically alternately, so that a fabric texture will not
form after elution of the sacrificial yarns 24.
[0082] The total density of the reinforcing yarns 22 and the
sacrificial yarns 24 is preferably from 176 to 850 yarns/inch, more
preferably from 198 to 850 yarns/inch, particularly preferably from
220 to 750 yarns/inch, more particularly preferably 220 to 442
yarns/inch, most particularly preferably 220 to 390 yarns/inch,
from the viewpoint of less likeliness of misalignment.
[0083] The aperture ratio of the reinforcing material is preferably
from 60 to 90%, more preferably from 65 to 85%, further preferably
from 70 to 85%, particularly preferably from 75 to 85%. When the
aperture ratio of the reinforcing material is at least the lower
limit value, the membrane resistance of the ion exchange membrane 1
can be suppressed to be sufficiently low, and increase of the
electrolysis voltage can be sufficiently suppressed. When the
aperture ratio of the reinforcing material is at most the upper
limit value, the mechanical strength as a reinforcing material will
be sufficiently high.
[0084] The aperture ratio of the reinforcing material can be
determined from an optical photomicrograph.
[0085] The thickness of the reinforcing material 20 is preferably
from 40 to 160 .mu.m, more preferably from 60 to 150 .mu.m,
particularly preferably from 70 to 140 .mu.m, especially preferably
from 80 to 130 .mu.m. When the thickness of the reinforcing
material 20 is at least the lower limit value, the mechanical
strength as a reinforcing material will be sufficiently high. When
the thickness of the reinforcing member 20 is at most the upper
limit value, the thickness at the yarn intersections can be
suppressed, and it is possible to sufficiently suppress the
influence to raise the electrolysis voltage due to current
shielding by the reinforcing material 20.
(Reinforcing Yarns)
[0086] The reinforcing yarns 22 are preferably ones having
durability against high temperature conditions in the alkali
chloride electrolysis, as well as against chlorine, sodium
hypochlorite and sodium hydroxide. As the reinforcing yarns 22,
from the viewpoint of mechanical strength, heat resistance and
chemical resistance, yarns comprising a fluoropolymer are
preferred; yarns comprising a perfluorocarbon polymer are more
preferred; yarns comprising PTFE are further preferred; and PTFE
yarns composed solely of PTFE are especially preferred.
[0087] The reinforcing yarns 22 may be monofilaments or may be
multifilaments. In a case where the reinforcing yarns 22 are PTFE
yarns, from such a viewpoint that spinning is easy, monofilaments
are preferred, and tape yarns obtained by slitting a PTFE film are
more preferred.
[0088] The fineness of the reinforcing yarns 22 is preferably from
50 to 200 denier, more preferably from 80 to 150 denier. When the
fineness of the reinforcing yarns 22 is at least the lower limit
value, the mechanical strength will be sufficiently high. When the
fineness of the reinforcing yarns 22 is at most the upper limit
value, the membrane resistance of the ion exchange membrane 1 can
be suppressed sufficiently low, and increase of the electrolysis
voltage can be sufficiently suppressed. Further, the reinforcing
yarns 22 will be less likely to be too close to the surface of the
electrolyte membrane 10, whereby cracking is less likely to enter
the surface of the electrolyte membrane 10, and as a result,
lowering of the mechanical strength can be prevented.
[0089] The width of the reinforcing yarns 22 in a cross section to
the length direction of the reinforcing yarns, i.e., as viewed from
a direction perpendicular to the reinforcing fabric forming the
reinforcing material 20, is from 70 to 160 .mu.m, preferably from
90 to 150 .mu.m, more preferably from 100 to 130 .mu.m. When the
width of the reinforcing yarns 22 is at least the above lower limit
value, the membrane strength of the ion exchange membrane 1 tends
to be high. When the width of the reinforcing yarns 22 is at most
the upper limit value, it is easy to lower the membrane resistance
of the ion exchange membrane 1, and easy to prevent increase in the
electrolysis voltage.
(Sacrificial Yarns)
[0090] The sacrificial yarns 24 will form elution holes as at least
a portion of the material is eluted in an alkaline aqueous solution
in the following step (i) for producing an ion exchange membrane.
The ion exchange membrane obtained via the step (i) is then placed
in an electrolytic cell, and prior to the main operation of alkali
chloride electrolysis, a conditioning operation of the following
step (ii) is carried out. Even in a case where sacrificial yarns 24
remaining undissolved in step (i) are present, in the step (ii),
the majority or preferably the entirety of the remaining material
of the sacrificial yarns 24 is eluted and removed in the alkaline
aqueous solution.
[0091] Here, the ion exchange membrane for alkali chloride
electrolysis of the present invention is a membrane produced via
the step (i) and disposed in an electrolytic cell in the step (ii),
and is not a membrane after the conditioning operation in the step
(ii).
[0092] Step (i): a step of immersing a reinforcing precursor
membrane having a reinforcing fabric embedded in a fluoropolymer
having groups convertible to ion exchange groups, in an alkaline
aqueous solution, to convert the fluoropolymer having groups
convertible to ion exchange groups, to a fluoropolymer having ion
exchange groups.
[0093] Step (ii): a step of disposing the ion exchange membrane
obtained via the step (i) in an electrolytic cell and carrying out
a conditioning operation before the main operation of alkali
chloride electrolysis.
[0094] As the sacrificial yarns 24, preferred are yarns comprising
at least one member selected from the group consisting of PET,
polybutylene terephthalate (hereinafter referred to as PBT),
polytrimethylene terephthalate (hereinafter referred to as PTT),
rayon and cellulose, and more preferred are PET yarns composed
solely of PET, PET/PBT yarns composed of a mixture of PET and PBT,
PBT yarns composed solely of PBT, or PTT yarns composed solely of
PTT.
[0095] As the sacrificial yarns 24, from the viewpoint of cost, PET
yarns are preferred. As the sacrificial yarns 24, from the
viewpoint that it is possible to obtain an ion-exchange membrane 1
which is hardly eluted in an alkaline aqueous solution during the
step (i) and which has sufficiently high mechanical strength, PBT
yarns or PTT yarns are preferred, and PTT yarns are particularly
preferred. As the sacrificial yarns 24, from the viewpoint of the
balance between costs and the mechanical strength of the ion
exchange membrane 1, PET/PBT yarns are preferred.
[0096] A sacrificial yarn 24 may be a monofilament formed from one
filament 26 or a multifilament having plural filaments 26 gathered
as shown in FIG. 1. A monofilament is preferable from the viewpoint
that yarn breakage is not likely to occur during weaving. A
multifilament is preferable from the viewpoint of easiness of to
being eluted in an alkaline aqueous solution.
[0097] In a case where a sacrificial yarn 24 is a multifilament,
the number of filaments per one sacrificial yarn 24 is preferably
from 2 to 32, more preferably from 2 to 16, further preferably from
2 to 8. When the number of filaments in the multifilament is at
least the above lower limit value, during the step (ii), a
sacrificial yarn 24 will be easily eluted in the alkaline aqueous
solution. When the number of filaments in the multifilament is at
most the above upper limit value, during the step (i), such a
sacrificial yarn will be hardly eluted in the alkaline aqueous
solution, and part of the sacrificial yarn will remain, whereby an
ion-exchange membrane 1 having sufficiently high mechanical
strength will be obtainable.
[0098] The fineness of the sacrificial yarns 24 is preferably from
6 to 14 denier, more preferably from 7 to 12 denier, prior to
elution of the sacrificial yarns 24 in the step (i). When the
fineness of the sacrificial yarns 24 is at least the above lower
limit value, the mechanical strength will be sufficiently high,
and, at the same time, weaving properties will be sufficiently
high. When the fineness of the sacrificial yarns 24 is at most the
above upper limit value, holes to be formed after the sacrificial
yarns 24 are eluted, are less likely to be too close to the surface
of the electrolyte membrane 10, and cracking is less likely to
occur at the surface of the electrolyte membrane 10, whereby
deterioration in the mechanical strength can be avoided.
(Elution Holes)
[0099] The ion exchange membrane 1 has, in the layer (S) (14a and
14b) of the electrolyte membrane 10, elution holes 28 formed by
elution of at least a portion of the material of the sacrificial
yarns 24 during the step (i) and the step (ii). As shown in FIG. 1,
in a case where a sacrificial yarn 24 is a monofilament composed of
one filament, at least a portion of the material of the
monofilament will be eluted to form an elution portion comprising a
collection of one hole. In a case where a sacrificial yarn 24 is a
multifilament, at least a portion of the material of the
multifilament will be eluted to form an elution hole comprising a
collection of plural holes. In a case where in the step (i), a
portion of the sacrificial yarn 24 has remained without being
eluted, the remaining sacrifice yarn is present in the elution
hole.
[0100] In the ion exchange membrane 1, it is preferred that even
after the step (i), a portion of the sacrificial yarns 24 remains,
and elution holes 28 are formed around filaments 26 of the
sacrificial yarns 24. Thereby, breakage such as cracking is less
likely to occur in the ion exchange membrane 1, at the time of
handling the ion exchange membrane 1 after the production of the
ion exchange membrane 1 and before the conditioning operation of
the alkali chloride electrolysis, or at the time of installation of
the ion exchange membrane 1 in the electrolytic cell at the time of
the conditioning operation.
[0101] Even if a portion of sacrificial yarns 24 remains after the
step (i), during the step (ii), the sacrificial yarns 24 will be
completely eluted in the alkaline aqueous solution and will be
removed, so that at the time of the main operation of the alkali
chloride electrolysis using the ion exchange membrane 1, they
present no influence over the membrane resistance. After the
installation of the ion exchange membrane 1 in the electrolytic
cell, there will be no large force to be exerted from outside to
the ion exchange membrane 1, and therefore, even if the sacrificial
yarns 24 have been completely eluted and removed in the alkaline
aqueous solution, it is less likely that breakage such as cracking
occurs in the ion exchange membrane.
[0102] Otherwise, in the present invention, all of the sacrificial
yarns 24 may be eluted in the entirety of sacrificial yarns 24 may
be eluted during the step (i) so that elution holes 28 can form
without remaining sacrificial yarns 24 prior to the step (ii).
[0103] In a cross section perpendicular to the length direction of
the reinforcing yarns of the ion exchange membrane 1, the total
area (S) obtained by adding the cross-sectional area of an elution
hole 28 and the cross-sectional area of a sacrificial yarn 24 in
the elution hole 28, is from 500 to 1,200 .mu.m.sup.2, preferably
from 550 to 1,100 .mu.m.sup.2, more preferably from 600 to 1,000
.mu.m.sup.2, further more preferably from 600 to 900 .mu.m.sup.2,
particularly preferably from 600 to 800 .mu.m.sup.2, per elution
hole. In a case where the sacrificial yarns are completely eluted,
the total area (S) becomes a cross-sectional area of only the
elution hole. That is, the total area (S) obtained by adding the
cross-sectional areas, becomes to be almost equal to the total area
of the cross-sectional area of one sacrificial yarn in the
reinforcing fabric. In a case where a sacrificial yarn is a
monofilament, the total area (S) becomes the cross-sectional area
of the elution hole formed from one filament, and in a case where a
sacrificial yarn is a multifilament composed of two or more
filaments, the total area (S) becomes the sum of the
cross-sectional areas of elution holes formed from the respective
filaments constituting the multifilament.
[0104] When the total area (S) is at least the above lower limit
value, it is possible to prepare a reinforcing fabric without
causing yarn breakage of the sacrificial yarns during weaving, and
it is possible to reduce the electrolysis voltage during the alkali
chloride electrolysis. When the total area (S) is at most the above
upper limit value, the hole formed after the sacrificial yarn 24 is
eluted will not be too close to the surface of the electrolyte
membrane 10, whereby cracking is less likely to enter the surface
of the electrolyte membrane 10, and as a result, lowering of the
mechanical strength can be prevented.
[0105] The total area (S) is measured by using an imaging software
by observing the cross section of the ion exchange membrane dried
at 90.degree. C. over 2 hours, by an optical electron
microscope.
[0106] In the present invention, in a cross section perpendicular
to the length direction of the reinforcing yarns forming a
reinforcing material, the total area (S) is in the above range. A
cross section perpendicular to the length direction of the
reinforcing yarns means at least one cross section selected from a
cross section (hereinafter referred to as "MD cross section") cut
perpendicular to the MD direction and a cross section (hereinafter
referred to as "TD cross section") cut perpendicular to the TD
direction, of the ion exchange membrane. That is, at least one of
the total area (S) of the total area (S) in the TD cross section
and the total area (S) in the MD cross section, is in the above
range.
[0107] Further, the MD cross-section of the ion-exchange membrane
in the present invention is preferably a cross section which does
not overlap with the reinforcing yarns, the sacrificial yarns and
the elution holes, disposed perpendicularly to the MD direction in
the reinforcing material embedded in the ion exchange membrane. The
same applies to the TD cross section.
[0108] The total area (S) in the cross section of the present
invention is more preferably such that the average value of the
total area (S) in the MD cross section and the total area (S) in
the TD cross section, is within the above range, further preferably
such that both of the total area (S) in the MD cross section and
the total area (S) in the TD cross section are within the above
range.
[0109] The total area (S) in the MD cross section can be obtained
by measuring the total area (S) with respect to elution holes at 10
locations randomly selected in the MD cross section of an ion
exchange, and obtaining the average value thereof. The total area
(S) in the TD cross section can be obtained also in the same
manner.
[0110] In an ion exchange membrane, in a case where a sacrificial
yarn is completely dissolved, the total area (S) is the
cross-sectional area of the elution hole, and in a case where a
sacrificial yarn remaining undissolved is present in an elution
hole, the total area (S) is a total area obtained by adding the
cross-sectional area of the elution hole and the cross-sectional
area of the sacrificial yarn remaining undissolved.
[0111] In a cross section perpendicular to the length direction of
the reinforcing yarns of the ion exchange membrane 1, the number n
of elution holes 28 between adjacent reinforcing yarns 22 is at
least 10, preferably from 10 to 20, particularly preferably from 10
to 12. When the number n of elution holes 28 is at least 10, it is
possible to reduce the electrolysis voltage during the alkaline
chloride electrolysis, while increasing the membrane strength.
Here, an elution hole formed from one sacrificial yarn made of a
multifilament is counted as 1.
[0112] The ion-exchange membrane of the present invention is a
membrane in which the distances of reinforcing yarns and elution
holes are within the above ranges, and the distance of elution
holes is within the above range, but it is particularly preferably
an ion exchange membrane having a structure wherein the distances
of reinforcing yarns and elution holes, and the number of elution
holes are in a relationship satisfying certain conditions, i.e. a
structure wherein the distance of reinforcing yarns, and the number
and distance of elution holes have a certain regularity.
[0113] That is, with respect to the distance of elution holes in
the ion exchange membrane of the present invention, the average
distance (d2) from the center of an elution hole 28 to the center
of the adjacent elution hole 28 in a cross section perpendicular to
the length direction of the reinforcing yarns of the ion-exchange
membrane 1, preferably satisfies the following relation (1), more
preferably satisfies the following relation (1-1), further
preferably satisfies the following formula (1-2), particularly
preferably satisfies the following formula (1-3). Thereby, it
becomes easy to obtain the effect of reducing the electrolysis
voltage during the alkali chloride electrolysis while increasing
the membrane strength.
0.5.ltoreq.{d2/d1.times.(n+1)}.ltoreq.1.5 (1)
0.7.ltoreq.{d2/d1.times.(n+1)}.ltoreq.1.4 (1-1)
0.8.ltoreq.{d2/d1.times.(n+1)}.ltoreq.1.2 (1-2)
0.8.ltoreq.{d2/d1.times.(n+1)}.ltoreq.1.0 (1-3)
wherein
[0114] d1: the average distance from the center of a reinforcing
yarn to the center of the adjacent reinforcing yarn,
[0115] d2: the average distance from the center of an elution hole
to the center of the adjacent elution hole,
[0116] n: number of elution holes between adjacent reinforcing
yarns.
[0117] In the present invention, in a cross section perpendicular
to the length direction of the reinforcing yarns, it is preferred
that the average distance (d1) and the average distance (d2)
satisfy the relationships of the above formulas. A cross section
perpendicular to the length direction of the reinforcing yarns
means at least one cross section selected from the MD cross section
and the TD cross section of the ion exchange membrane. That is, the
average distance (d1) and the average distance (d2) in at least one
cross section selected from the MD cross section and the TD cross
section preferably satisfy the relationships of the above
formulas.
[0118] In the present invention, it is preferred that an average
value of the average distance (d1) in the MD cross section and the
average distance (d1) in the TD cross section, and an average value
of the average distance (d2) in the MD cross section and the
average distance (d2) in the TD cross section, satisfy the above
formulas, and it is more preferred that in both the MD cross
section and the TD cross section, the average distance (d1) and the
average distance (d2) satisfy the relationships of the above
formulas.
[0119] The values of the average distance (d1) and the average
distance (d2) in the MD cross section, are obtainable by measuring,
in the MD cross section of the ion exchange membrane, the average
distance (d1) and the average distance (d2), respectively, at 10
locations randomly selected, and obtaining the respective average
values. The average distance (d1) and the average distance (d2) in
the TD cross section are obtainable in the same manner.
[0120] In the present invention, in a cross section perpendicular
to the length direction of the reinforcing yarns of the ion
exchange membrane, all the distance (d2') from the center of an
elution hole to the center of the adjacent elution hole, preferably
satisfy the relation of the following formula (1'), more preferably
satisfies the relation of the following formula (1'-1), further
preferably satisfies the relation of the following formula (1'-2),
particularly preferably satisfies the relation of the following
formula (1'-3), at all of the measurement points measured to
determine the average distance (d2). Thereby, it becomes easy to
obtain the effect of reducing the electrolysis voltage during the
alkali chloride electrolysis, while increasing the membrane
strength.
[0121] Here, in the distance (d2'), all of the measurement points
measured to determine the average distance (d2) mean all of the
measurement points measured to calculate the average distance (d2).
Specifically, in the MD cross section or the TD cross section, all
of the measurement points mean the measurement points at 10
locations measured to obtain the average distance (d2).
0.5.ltoreq.{d2'/d1.times.(n+1)}.ltoreq.1.5 (1')
0.7.ltoreq.{d2'/d1.times.(n+1)}.ltoreq.1.4 (1'-1)
0.8.ltoreq.{d2'/d1.times.(n+1)}.ltoreq.1.2 (1'-2)
0.8.ltoreq.{d2'/d1.times.(n+1)}.ltoreq.1.0 (1'-3)
provided that the symbols in the formula (1') have the following
meanings,
[0122] d2': the distance from the center of an elution hole to the
center of the adjacent elution hole,
[0123] d1 and n: the same as above.
[0124] Further, with respect to the distance between a reinforcing
yarn and an elution hole in the ion exchange membrane of the
present invention, in a cross section perpendicular to the length
direction of the reinforcing yarns of the ion exchange membrane 1,
an average distance (d3) from the center of a reinforcing yarn 22
to the center of the adjacent elution hole 28 preferably satisfies
the relation of the following formula (2), more preferably
satisfies the relation of the following formula (2-1), further
preferably satisfies the relation of the following formula (2-2).
Thereby, it becomes easy to obtain the effect of reducing the
electrolysis voltage during the alkali chloride electrolysis, while
increasing the membrane strength.
1.0.ltoreq.{d3/d1.times.(n+1)}.ltoreq.2.0 (2)
1.2.ltoreq.{d3/d1.times.(n+1)}.ltoreq.1.8 (2-1)
1.5.ltoreq.{d3/d1.times.(n+1)}.ltoreq.1.8 (2-2)
provided that the symbols in the formula (2) have the following
meanings:
[0125] d3: the average distance from the center of a reinforcing
yarn to the center of the adjacent elution hole.
[0126] d1 and n: the same as above.
[0127] Further, in the present invention, in a cross section
perpendicular to the length direction of the reinforcing yarns, the
average distance (d1) and the average distance (d3) preferably
satisfy the relations of the above formulas. A cross section
perpendicular to the length direction of the reinforcing yarns
means at least one cross section of the MD cross section and the TD
cross section of the ion exchange membrane. That is, the average
distance (d1) and the average distance (d3) in at least one cross
section selected from the MD cross section and the TD cross section
preferably satisfy the relations of the above formulas.
[0128] In the present invention, it is preferred that an average
value of the average distance (d1) in the MD cross section and the
average distance (d1) in the TD cross section, and an average value
of the average distance (d3) in the MD cross section and the
average distance (d3) in the TD cross section, satisfy the above
formulas, and it is more preferred that in both the MD cross
section and the TD cross section, the average distance (d1) and the
average distance (d3) satisfy the relations of the above
formulas.
[0129] The values of the average distance (d1) and the average
distance (d3) in the MD cross section are obtainable by measuring,
in the MD cross section of the ion exchange membrane, the average
distance (d1) and the average distance (d3) at 10 locations
randomly selected, and obtaining the respective average values. The
average distance (d1) and the average distance (d3) in the TD cross
section are obtainable also in the same manner.
[0130] In the present invention, in a cross section perpendicular
to the length direction of the reinforcing yarns of the ion
exchange membrane, the distance (d3') from the center of a
reinforcing yarn to the center of the adjacent elution hole,
preferably satisfies the relation of the following formula (2'),
more preferably satisfies the relation of the following formula
(2'-1), further preferably satisfies the relation of the following
formula (2'-2), at all of the measurement points. Thereby, it
becomes easy to obtain the effect of reducing the electrolysis
voltage during the alkali chloride electrolysis, while increasing
the membrane strength. Here, in the distance d3', all of the
measurement points measured to determine the average distance (d3)
mean all of the measurement points measured to calculate the
average distance (d3). Specifically, in an optional MD cross
section or TD cross section, they mean measurement points at 10
locations measured to obtain the average distance (d3).
1.0.ltoreq.{d3'/d1.times.(n+1)}.ltoreq.2.0 (2')
1.2.ltoreq.{d3'/d1.times.(n+1)}.ltoreq.1.8 (2'-1)
1.5.ltoreq.{d3'/d1.times.(n+1)}.ltoreq.1.8 (2'-2)
provided that the symbols in the formula (2') have the following
meanings,
[0131] d3': the distance from the center of an elution hole to the
center of the adjacent elution hole,
[0132] d1 and n: the same as above.
[Production Method]
[0133] The ion exchange membrane 1 in the present invention is
preferably produced via the above step (i), and the step (i)
preferably comprises the following steps (a) and (b).
[0134] Step (a): a step of obtaining a reinforcing precursor
membrane by embedding a reinforcing fabric made of reinforcing
yarns and sacrificial yarns, in a fluoropolymer having groups
convertible to ion exchange groups,
[0135] Step (b): a step of contacting the reinforcing precursor
membrane obtained in the step (a) to an alkaline aqueous solution
to convert the fluoropolymer having groups convertible to ion
exchange groups, to a fluoropolymer having ion exchange groups and
at the same time, to let at least a portion of the sacrificial
yarns of the embedded reinforcing fabric, elute, thereby to obtain
an ion exchange membrane 1 comprising a fluoropolymer having ion
exchange groups, a reinforcing material having at least a portion
of the sacrificial yarns in the reinforcing fabric eluted, and
elution holes.
[0136] Here, in the step (b), after converting the groups
convertible to ion exchange groups, to ion exchange groups, if
necessary, salt exchange to replace the counter cation of the ion
exchange groups may be carried out. In the salt exchange, the
counter cation of the ion exchange group may be replaced, for
example, from potassium to sodium.
(Step (a))
[0137] In the step (a), firstly, by a co-extrusion method, a
laminated membrane comprising a layer (hereinafter referred to as
"layer (C')") made of a fluoropolymer having groups convertible to
carboxylic acid functional groups, and a layer (hereinafter
referred to as "layer (S')") made of a fluoropolymer having groups
convertible to sulfonic acid functional groups, is obtained.
Further, separately, by a single layer extrusion process, a
membrane (hereinafter referred to as "membrane (S')") made of a
layer (S') of a fluoropolymer having groups convertible to sulfonic
acid functional groups, is obtained.
[0138] Then, the membrane (S'), a reinforcing fabric and the
laminated membrane are disposed in this order and laminated by
means of a laminating roll or vacuum laminating apparatus. At that
time, the laminated membrane of the laminated membrane (S') and the
layer (C') is disposed so that the layer (S') is in contact with
the reinforcing fabric.
(Fluoromonomers Having Groups Convertible to Carboxylic Acid
Functional Groups)
[0139] The fluoropolymer (C') to form the layer (C') may, for
example, be a copolymer having units derived from a fluoromonomer
(hereinafter referred to as "a fluoromonomer (C')") having a group
convertible to a carboxylic acid functional group and units derived
from a fluorinated olefin.
[0140] The fluoromonomer (C') is not particularly limited so long
as it is a compound having one or more fluorine atoms in the
molecule, an ethylenic double bond, and a group convertible to a
carboxylic acid functional group, and it is possible to use a
conventional one.
[0141] As the fluoromonomer (C'), a fluorovinyl ether represented
by the following formula (3) is preferred from the viewpoint of the
production cost of the monomer, the reactivity with other monomers
and excellent properties of the obtainable fluoropolymer.
CF.sub.2.dbd.CF--(O).sub.p--(CF.sub.2).sub.q--(CF.sub.2CFX).sub.r--(O).s-
ub.s--(CF.sub.2).sub.t--(CF.sub.2CFX').sub.u-A.sup.1 (3)
[0142] In the formula (3), X is a fluorine atom or a
trifluoromethyl group. X' is a fluorine atom or a trifluoromethyl
group. X and X' in the formula (3) may be the same or
different.
[0143] A.sup.1 is a group convertible to a carboxylic acid
functional group. The group convertible to a carboxylic acid
functional group is a functional group which can be converted to a
carboxylic acid functional group by hydrolysis. As the group
convertible to a carboxylic acid functional group, for example,
--CN, --COF, --COOR.sup.1 (wherein R.sup.1 is a C.sub.1-10 alkyl
group), --COONR.sup.2R.sup.3 (wherein R.sup.2 and R.sup.3 are each
a hydrogen atom or a C.sub.1-10 alkyl group, and R.sup.2 and
R.sup.3 may be the same or different), etc., may be mentioned.
[0144] p is 0 or 1, q is an integer from 0 to 12, r is an integer
of from 0 to 3, s is 0 or 1, t is an integer from 0 to 12, and u is
an integer of from 0 to 3. However, p and s are not 0 at the same
time, and r and u are not 0 at the same time. That is,
1.ltoreq.p+s, and 1.ltoreq.r+u.
[0145] As specific examples of the fluorovinyl ether of the formula
(3), the following compounds may be mentioned, and, from the
viewpoint of easy production, a compound wherein p=1, q=0, r=1, s=0
to 1, t=1 to 3 and u=0 to 1, is preferred.
[0146] CF.sub.2.dbd.CF--O--CF.sub.2CF.sub.2--COOCH.sub.3,
[0147]
CF.sub.2.dbd.CF--O--CF.sub.2CF.sub.2--CF.sub.2--COOCH.sub.3,
[0148]
CF.sub.2.dbd.CF--O--CF.sub.2CF.sub.2--CF.sub.2CF.sub.2--COOCH.sub.3-
,
[0149]
CF.sub.2.dbd.CF--O--CF.sub.2CF.sub.2--O--CF.sub.2CF.sub.2--COOCH.su-
b.3,
[0150]
CF.sub.2.dbd.CF--O--CF.sub.2CF.sub.2--O--CF.sub.2CF.sub.2--CF.sub.2-
--COOCH.sub.3,
[0151]
CF.sub.2.dbd.CF--O--CF.sub.2CF.sub.2--O--CF.sub.2CF.sub.2--CF.sub.2-
CF.sub.2--COOCH.sub.3,
[0152]
CF.sub.2.dbd.CF--O--CF.sub.2--CF.sub.2CF.sub.2--O--CF.sub.2CF.sub.2-
--COOCH.sub.3,
[0153]
CF.sub.2.dbd.CF--O--CF.sub.2CF(CF.sub.3)--O--CF.sub.2CF.sub.2--COOC-
H.sub.3,
[0154]
CF.sub.2.dbd.CF--O--CF.sub.2CF(CF.sub.3)--O--CF.sub.2--CF.sub.2CF.s-
ub.2--COOCH.sub.2.
[0155] As the fluoromonomer (C'), one type may be used alone, or
two or more types may be used in combination.
[0156] The fluorinated olefin may, for example, be a C.sub.2-3
fluoroolefin having one or more fluorine atoms in the molecule. As
such a fluoroolefin, tetrafluoroethylene (CF.sub.2.dbd.CF.sub.2)
(hereinafter referred to as TFE), chlorotrifluoroethylene
(CF.sub.2.dbd.CFCl), vinylidene fluoride (CF.sub.2.dbd.CH.sub.2),
vinyl fluoride (CH.sub.2.dbd.CHF), hexafluoropropylene
(CF.sub.2.dbd.CFCF.sub.3), etc. may be mentioned. Among them, TFE
is particularly preferred from the viewpoint of the production cost
of the monomer, the reactivity with other monomers and excellent
properties of the obtainable fluoropolymer.
[0157] As the fluorinated olefin, one type may be used alone, or
two or more types may be used in combination.
[0158] For the production of the fluoropolymer (C') to form the
layer (C'), in addition to the fluoromonomer (C') having a group
convertible to a carboxylic acid functional group and the
fluorinated olefin, other monomers may further be used. Such other
monomers may, for example, be CF.sub.2.dbd.CF--R.sup.f (wherein
R.sup.f is a perfluoroalkyl group having from 2 to 10 carbon
atoms), CF.sub.2.dbd.CF--OR.sup.f1 (wherein R.sup.f1 is a
perfluoroalkyl group having from 1 to 10 carbon atoms),
CF.sub.2.dbd.CFO(CF.sub.2).sub.vCF.dbd.CF.sub.2 (wherein v is an
integer of from 1 to 3), etc. By copolymerizing other monomers, it
is possible to improve flexibility and mechanical strength of the
ion exchange membrane 1. The proportion of other monomers is
preferably at most 30 mass % in the total monomers (100 mass %),
from the viewpoint of maintaining the ion exchange performance.
[0159] The ion exchange capacity of the fluoropolymer (C) is
preferably from 0.5 to 2.0 meq/g dry resin. The ion exchange
capacity of the fluoromonomer (C') having a group convertible to a
carboxylic acid functional group is preferably at least 0.6 meq/g
dry resin, more preferably at least 0.7 meq/g dry resin, from the
viewpoint of mechanical strength and electrochemical performance as
an ion exchange membrane.
[0160] In order to bring the ion exchange capacity of the
fluoropolymer (C') to be within the above range, the content of
units derived from a fluoromonomer (C') in the fluoropolymer (C')
may be made so that the ion-exchange capacity of the fluoropolymer
(C') will be within the above range after converting the groups to
be convertible to carboxylic acid functional groups in the
fluoropolymer (C') to carboxylic acid functional groups. The
content of carboxylic acid functional groups in the fluoropolymer
(C') is preferably the same as the content of the groups
convertible to carboxylic acid functional groups in the
fluoropolymer (C').
[0161] With respect to the molecular weight of the fluoropolymer
(C'), from the viewpoint of mechanical strength and film-forming
ability as an ion exchange membrane, the TQ value is preferably
150.degree. C., more preferably from 170 to 340.degree. C., further
preferably from 170 to 300.degree. C.
[0162] The TQ value is a value related to the molecular weight of a
polymer, and is one represented by a temperature showing a volume
flow rate: 100 mm.sup.3/sec. The volume flow rate is one obtained
by letting a polymer be melted and flow out from an orifice
(diameter: 1 mm, length: 1 mm) at a constant temperature under a
pressure of 3 MPa and representing the amount of the flowing out
polymer by a unit of mm.sup.3/sec. The TQ value serves as an index
for the molecular weight of the polymer and indicates that the
higher the TQ value, the higher the molecular weight.
(Fluoropolymers Having Groups Convertible to Sulfonic Acid
Functional Groups)
[0163] The fluoropolymer (S') to form the layer (S') may, for
example, be a copolymer having units derived from a fluoromonomer
having a group convertible to a sulfonic acid functional group
(hereinafter referred to as "a fluoromonomer (S')" and units
derived from a fluorinated olefin.
[0164] The fluoromonomer (S') is not particularly limited so long
as it has one or more fluorine atoms in the molecule, an ethylenic
double bond and a group convertible to a sulfonic acid functional
group, and a conventional one may be employed.
[0165] As the fluoromonomer (S'), from the viewpoint of the
production cost of the monomer, the reactivity with other monomers
and excellent properties of the obtainable fluoropolymer, a
compound represented by the following formula (4) or a compound
represented by the following formula (5) is preferred.
CF.sub.2.dbd.CF--O--R.sup.f2-A.sup.2 (4),
CF.sub.2.dbd.CF--R.sup.f2-A.sup.2 (5).
[0166] R.sup.f2 is a perfluoroalkylene group having from 1 to 20
carbon atoms, may contain an etheric oxygen atom, and may be
straight-chained or branched.
[0167] A.sup.2 is a group convertible to a sulfonic acid functional
group. The group convertible to a sulfonic acid functional group is
a functional group that can be converted to a sulfonic acid
functional group by hydrolysis. The functional group that can be
converted to a sulfonic acid functional group may, for example, be
--SO.sub.2F, --SO.sub.2Cl, --SO.sub.2Br, etc.
[0168] As the compound represented by the formula (4), the
following compounds are specifically preferred.
[0169] CF.sub.2.dbd.CF--O--(CF.sub.2).sub.a--SO.sub.2F (wherein a
is an integer of from 1 to 8),
[0170]
CF.sub.2.dbd.CF--O--CF.sub.2CF(CF.sub.3)O(CF.sub.2).sub.a--SO.sub.2-
F (wherein a is an integer of from 1 to 8),
[0171] CF.sub.2.dbd.CF[OCF.sub.2CF(CF.sub.3)].sub.aSO.sub.2F
(wherein a is an integer of from 1 to 5).
[0172] As the compound represented by the formula (5), the
following compounds are specifically preferred.
[0173] CF.sub.2.dbd.CF(CF.sub.2).sub.b--SO.sub.2F (wherein b is an
integer of from 1 to 8),
[0174] CF.sub.2.dbd.CF--CF.sub.2--O--(CF.sub.2).sub.b--SO.sub.2F
(wherein b is an integer of from 1 to 8).
[0175] As the fluoromonomer (S'), from such a viewpoint that
industrial synthesis is easy, the following compounds are more
preferred.
[0176] CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F,
[0177] CF.sub.2.dbd.CFOCF.sub.2CF.sub.2CF.sub.2SO.sub.2F,
[0178]
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2CF.sub.2CF.sub.2SO.sub.2F,
[0179]
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.2SO.sub.2F,
[0180]
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.2CF.sub.2SO.sub-
.2F,
[0181] CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)SO.sub.2F,
[0182] CF.sub.2.dbd.CFCF.sub.2CF.sub.2SO.sub.2F,
[0183] CF.sub.2.dbd.CFCF.sub.2CF.sub.2CF.sub.2SO.sub.2F,
[0184]
CF.sub.2.dbd.CF--CF.sub.2--O--CF.sub.2CF.sub.2--SO.sub.2F.
[0185] As the fluoromonomer (S'), one type may be used alone, or
two or more types may be used in combination.
[0186] The fluorinated olefin may be those exemplified above, and
from the viewpoint of the production cost of the monomer, the
reactivity with other monomers and excellent properties of the
obtainable fluoropolymer, TFE is particularly preferred.
[0187] As the fluorinated olefin, one type may be used alone, or
two or more types may be used in combination.
[0188] For the production of the fluoropolymer (S') to form the
layer (S'), in addition to the fluoromonomer (S') and the
fluorinated olefin, other monomers may further be used.
[0189] Such other monomers may be those exemplified above. By
copolymerizing other monomers, it is possible to improve
flexibility and mechanical strength of the ion exchange membrane 1.
The proportion of other monomers is preferably at most 30 mass % in
all monomers (100 mass %), from the viewpoint of maintaining the
ion exchange performance.
[0190] The ion exchange capacity of the fluoropolymer (S') is
preferably from 0.5 to 2.0 meq/g dry resin. The ion exchange
capacity of the fluoropolymer (S') is preferably at least 0.6 meq/g
dry resin, more preferably at least 0.7 meq/g dry resin, from the
viewpoint of mechanical strength and electrochemical performance as
an ion exchange membrane.
[0191] In order to bring the ion exchange capacity of the
fluoropolymer (S) to be within the above range, the content of
units derived from a fluoromonomer (S') in the fluoropolymer (S')
may be adjusted so that the ion exchange capacity of the
fluoropolymer (S) will be within the above range, after converting
the groups convertible to sulfonic acid functional groups in the
fluoropolymer (S') to sulfonic acid functional groups. The content
of sulfonic acid functional groups in the fluoropolymer (S) is
preferably the same as the content of the groups convertible to
sulfonic acid functional groups in the fluoropolymer (S').
[0192] With respect to the molecular weight of the fluoropolymer
(S'), from the viewpoint of mechanical strength and
membrane-forming ability as an ion exchange membrane, the TQ value
is preferably at least 150.degree. C., more preferably from 170 to
340.degree. C., further preferably from 170 to 300.degree. C.
(Step (b))
[0193] An ion exchange membrane 1 is obtained by convert at least a
portion of the groups convertible to carboxylic acid functional
groups and the groups convertible to sulfonic acid functional
groups in the reinforcing precursor membrane obtained in the above
step (a), to carboxylic acid functional groups and sulfonic acid
functional groups, respectively. The method for hydrolysis may, for
example, be preferably a method of using a mixture of a
water-soluble organic compound and a hydroxide of an alkali metal,
as described in e.g. JP-A-H03-6240.
[0194] In the step (b), by contacting the reinforcing precursor
membrane to an alkaline aqueous solution, at least a portion of
sacrificial yarns 24 is eluted by hydrolysis in the alkaline
aqueous solution. The elution of sacrificial yarns 24 is preferably
carried out by hydrolysis of the material constituting the
sacrificial yarns.
Advantageous Effects
[0195] In a case where an ion exchange membrane is reinforced by a
reinforcing material formed of reinforcing yarns and optionally
contained sacrificial yarns, it is considered that the reinforcing
yarns will prevent migration of cations such as sodium ions in the
membrane, whereby the vicinity on the cathode side of the
reinforcing yarns will be a region (hereinafter referred to as a
current-shielding region) not substantially functioning as an
electrolysis site. Therefore, if the density of the reinforcing
yarns is increased by narrowing their spacing, the
current-shielding region within the ion exchange membrane will be
increased, whereby it is considered the membrane resistance will
increase, and the electrolysis voltage becomes high.
[0196] Whereas, in the ion exchange membrane for alkali chloride
electrolysis of the present invention, the above-mentioned average
distance (d1), the total area (S) and the number (n) of elution
holes, are controlled to be within the specific ranges, whereby
even if the membrane strength is increased by narrowing the spacing
of reinforcing yarns, the membrane resistance is kept low, and it
is possible to reduce the electrolysis voltage at the time of
alkali chloride electrolysis. This is considered to be as
follows.
[0197] When the total area (S) is small, sodium ions, etc. tend to
be difficult to pass through portions of elution holes in the
vicinity of the reinforcing yarns, whereby the membrane resistance
in the vicinity of the reinforcing yarns tends to be higher than
when the total area (S) is large. On the other hand, at a portion
apart from reinforcing yarns, the volume of elution holes is small
as compared to when the total area (S) is large, whereby extra
resistance will not increase, and the membrane resistance tends to
be low. Further, when the above total area (S) is large, sodium
ions, etc. tend to easily pass together with the salt water through
elution holes in the vicinity of reinforcing yarns, and the current
shielding region becomes smaller, whereby the membrane resistance
in the vicinity of reinforcing yarns becomes low as compared to
when the total area (S) is small. On the other hand, at a portion
apart from reinforcing yarns, the volume of elution holes is larger
than when the total area (S) is small, whereby extra resistance
tends to increase, and the membrane resistance tends to
increase.
[0198] Further, when the number (n) of elution holes is small, like
in the case where the total area (S) is small, sodium ions, etc.
tend to be difficult to pass in the vicinity of reinforcing yarns,
and the membrane resistance in the vicinity of reinforcing yarns
tend to be high as compared to when the number (n) of elution holes
is large. On the other hand, at a portion apart from reinforcing
yarns, the volume of elution holes is small, whereby extra
resistance will not increase, and the membrane resistance tends to
be low as compared to when the number (n) of elution holes is
large. Further, when the above-described number (n) of elution
holes is large, sodium ions, etc. tend to easily pass in the
vicinity of reinforcing yarns, and the current shielding region
becomes smaller, whereby the membrane resistance in the vicinity of
reinforcing yarns tends to be low as compared to when the number n
of elution holes is small. On the other hand, at a portion apart
from reinforcing yarns, the volume of elution holes increases,
whereby extra resistance will increase, and the membrane resistance
becomes high as compared to when the number n of elution holes is
small. From the foregoing, it is important to control the number
(n) of elution holes and the total area (S) to be within the
specific range.
[0199] If the spacing of reinforcing yarns is made to be too narrow
and the current shielded region within the ion exchange membrane
becomes extremely large, the effects to reduce the membrane
resistance by the total area (S) and the number (n) of elution
holes tend to be relatively small. On the other hand, if the
spacing of the reinforcing yarns is made to be too wide, and the
current shielding region becomes extremely small, elution holes
tend to be extra resistance, and the effect to reduce the
electrolysis voltage tends to be relatively small. Therefore, it is
important to control the spacing of reinforcing yarns to be within
the specific range.
[0200] In the present invention, by controlling the above-described
total area (S) and number n of elution holes within specific
ranges, the current shielding region in the vicinity of reinforcing
yarns is made small to lower the membrane resistance in the
vicinity of reinforcing yarns, and at the same time, the volume of
elution holes at a portion apart from reinforcing yarns is
maintained to be small to some extent, whereby increase in the
membrane resistance at this portion is suppressed. Thus, as
compared with the degree of increase in membrane resistance at a
portion apart from reinforcing yarns, the degree of decrease in the
membrane resistance in the vicinity of reinforcing yarns becomes
large, whereby it is considered that, as the entire membrane, the
membrane resistance becomes low, and even if the spacing of
reinforcing yarns is made narrow to increase the membrane strength,
it is possible to reduce the electrolysis voltage at the time of
alkali chloride electrolysis.
OTHER EMBODIMENTS
[0201] Further, the ion exchange membrane of the present invention
is not limited to the ion-exchange membrane 1 as described
above.
[0202] For example, the ion exchange membrane of the present
invention may be one wherein the electrolyte membrane is a membrane
of a single layer, or a laminate having layers other than the layer
(C) and the layer (S). Further, it may be one wherein the
reinforcing fabric is embedded in the layer (C).
[0203] Further, the sacrificial yarns are not limited to
monofilaments as illustrated in the drawings, and may be
multifilaments.
<Alkali Chloride Electrolysis Apparatus>
[0204] For the alkali chloride electrolysis apparatus of the
present invention, a known embodiment may be employed except for
using the ion exchange membrane for alkali chloride electrolysis of
the present invention. FIG. 3 is a schematic diagram showing an
example of the alkali chloride electrolysis apparatus of the
present invention.
[0205] The alkali chloride electrolysis apparatus 100 of this
embodiment comprises an electrolytic cell 110 provided with a
cathode 112 and an anode 114, and an ion exchange membrane 1
installed in the electrolytic cell 110 so as to partition inside of
the electrolytic cell 110 into a cathode chamber 116 on the cathode
112 side and an anode chamber 118 on the anode 114 side.
[0206] The ion exchange membrane 1 is installed in the electrolytic
cell 110 so that the layer (C) 12 is located on the cathode 112
side, and the layer (S) 14 is located on the anode 114 side.
[0207] The cathode 112 may be disposed in contact with the ion
exchange membrane 1 or may be disposed with a space from the ion
exchange membrane 1.
[0208] As the material constituting the cathode chamber 116,
preferred is a material which is resistant to sodium hydroxide and
hydrogen. As such a material, stainless steel, nickel, etc. may be
mentioned.
[0209] As the material constituting the anode chamber 118,
preferred is a material which is resistant to sodium chloride and
chlorine. As such a material, titanium may be mentioned.
[0210] For example, in a case where an aqueous solution of sodium
hydroxide is to be produced by electrolysis of a potassium chloride
aqueous solution, by supplying a sodium chloride aqueous solution
to the anode chamber 118 of the alkali chloride electrolysis
apparatus 100, and supplying a sodium hydroxide aqueous solution to
the cathode compartment 116, the sodium chloride aqueous solution
is electrolyzed while maintaining the concentration of the sodium
hydroxide aqueous solution discharged from the cathode chamber 116
at a predetermined concentration (e.g. 32 mass %).
[0211] According to the alkali chloride electrolysis apparatus of
the present invention as described above has the ion exchange
membrane for alkali chloride electrolysis of the present invention,
and thus the membrane strength is high, and it is possible to
reduce the electrolysis voltage during the alkaline chloride
electrolysis.
EXAMPLES
[0212] In the following, the present invention will be described in
detail with reference to Examples, but the present invention is not
limited by these Examples. Ex. 1 to 2, 5 and 8 are Examples of the
present invention, and Ex. 3, 4, 6 and 7 are Comparative
Examples.
[Measurement Method of TQ Value]
[0213] The TQ value is a value related to the molecular weight of a
polymer and was obtained as a temperature showing a volume flow
rate of 100 mm.sup.3/sec. The volume flow rate is a flow out amount
(unit: mm.sup.3/sec.) when a fluoropolymer having groups
convertible to ion exchange groups, is melted and permitted to flow
out from an orifice (diameter: 1 mm, length: 1 mm) at a constant
temperature under a pressure of 3 MPa, by using Shimadzu Flow
Tester CFD-100D (manufactured by Shimadzu Corporation).
[Measurement Method of Ion Exchange Capacity]
[0214] About 0.5 g of a fluoropolymer having groups convertible to
ion exchange groups was formed into a film by flat pressing, and
then, the film was analyzed by a transmission infrared spectroscopy
apparatus. The ratio of the units having groups convertible to
carboxylic acid functional groups or the units having groups
convertible to sulfonic acid functional groups was calculated by
using the respective peak heights of CF.sub.2 peak, CF.sub.3 peak,
OH peak, CF peak and SO.sub.2F peak, of the obtained spectra, and
this was regarded as the ratio of the units having carboxylic acid
functional groups or the units having sulfonic acid functional
groups in the fluoropolymer obtained after hydrolysis treatment.
Then, the ion exchange capacity was calculated by using known
samples as the calibration curve.
[0215] Further, a film having an ion exchange group whose terminal
group is acid type or K type or N type can be measured
similarly.
[Measurement Method of Distance of Reinforcing Yarns and Elution
Holes]
[0216] By observing a cross section of reinforcing yarns, of an ion
exchange membrane dried at 90.degree. C. for at least 2 hours in
the atmosphere by an optical microscope, the distance was measured
by using an image software (Pixs2000 PRO manufactured by INNOTECH
CORPORATION). In the measurement, in each of the MD cross section
and the TD cross section, the distance from the center of a
reinforcing yarn to the center of the adjacent reinforcing yarn was
measured at 10 points. With respect to the MD cross section, the
average distance (d1) being an average value of the measured values
at 10 points, was obtained. Also with respect to the TD cross
section, the average distance (d1) was obtained in the same
manner.
[0217] Further, the average distances (d2) and (d3) were obtained
in the same manner. The average distance d1 was obtained from the
average. The average values d2 and d3 were obtained in the same
manner.
[0218] Here, the average distances (d1), (d2) and (d3) are values
of a reinforcing material embedded in an ion exchange membrane
produced via the steps (a) and (b).
[Measurement Method of Cross-Sectional Area]
[0219] By observing a cross section cut perpendicular to the length
direction of reinforcing yarns, of an ion exchange membrane dried
at 90.degree. C. for at least 2 hours in the atmosphere by an
optical microscope, the total area (S) obtained by adding the
cross-sectional area of an elution hole and the cross-sectional
area of a sacrificial yarn, was measured by using an image software
(Pixs2000 PRO manufactured by INNOTECH CORPORATION). The total area
(S) was measured at 10 points randomly selected in each of the MD
cross section and the TD cross section. With respect to the MD
cross section, the total area (S) was obtained as an average value
of the measured values at 10 points. Also with respect to the TD
cross section, the total area (S) was obtained in the same
manner.
[0220] In a case where a sacrificial yarn is completely dissolved,
the total area (S) is the cross-sectional area of the elution hole,
and in a case where a sacrificial yarn remaining undissolved is
present in an elution hole, the total area (S) is a value obtained
by adding the cross-sectional area of the elution hole and the
cross-sectional area of the sacrificial yarn remaining
undissolved.
[Measurement Method of Width of Reinforcing Yarn]
[0221] By observing a cross section of an ion exchange membrane
dried at 90.degree. C. for at least 2 hours in the atmosphere by an
optical microscope, the width of a reinforcing fabric as viewed in
a direction perpendicular to the fabric surface of a reinforcing
material was measured by using an image software (Pixs2000 PRO
manufactured by INNOTECH CORPORATION). The width of the reinforcing
yarn was measured at 10 points in each of the MD cross section and
the TD cross section, and then the average value was obtained.
[Measurement of Aperture Ratio]
[0222] For the aperture ratio, by observing a cross section cut
perpendicular to the length direction of reinforcing yarns, of an
ion exchange membrane dried at 90.degree. C. for at least 2 hours
in the atmosphere by an optical microscope, the aperture ratio was
calculated by using an image software (Pixs2000 PRO manufactured by
INNOTECH CORPORATION). For the calculation, in each of the MD cross
section (cross section cut perpendicular to the MD direction) and
the TD cross section (cross section cut perpendicular to the TD
direction), the distance from the center of a reinforcing yarn to
the center of the adjacent reinforcing yarn, and the width of a
reinforcing yarn were measured at 10 points, and the aperture ratio
was calculated from the following formula.
{(Distance between reinforcing yarns in the MD cross section-width
of reinforcing yarn in the MD cross section).times.(distance
between reinforcing yarns in the TD cross section-width of
reinforcing yarn in the TD cross section)}/{(distance between
reinforcing yarns in the MD cross section).times.(distance between
reinforcing yarns in TD cross section)}.times.100
[Measurement Method of Electrolysis Voltage]
[0223] The ion exchange membrane was installed in a test
electrolytic cell with an electrolytic surface size of 150
mm.times.100 mm so that the layer (C) faced the cathode. DSE
manufactured by PERMELEC ELECTRODE LTD. was used as the anode, and
Raney nickel plating cathode manufactured by CHLORINE ENGINEERS was
used as the cathode. Electrolysis of a sodium chloride aqueous
solution was conducted under conditions of a sodium hydroxide
concentration of 32 mass %, a sodium chloride concentration of 200
g/L, a temperature of 90.degree. C. and a current density of 8
kA/m.sup.2, whereby the electrolysis voltage (V) was measured after
3 to 10 days from the initiation of operation.
[Ex. 1]
[0224] TFE and a fluoromonomer having groups convertible to
carboxylic acid functional groups, represented by the following
formula (3-1) were copolymerized to synthesize a fluoropolymer
having groups convertible to carboxylic acid functional groups (ion
exchange capacity: 1.06 meq/g dry resin, TO: 225.degree. C.)
(hereinafter referred to as polymer C).
CF.sub.2.dbd.CF--O--CF.sub.2CF.sub.2--CF.sub.2--COOCH.sub.3
(3-1).
[0225] TFE and a fluoromonomer having groups convertible to
sulfonic acid functional groups, represented by the following
formula (4-1) were copolymerized to synthesize a fluoropolymer
having groups convertible to sulfonic acid functional groups (ion
exchange capacity: 1.1 meq/g dry resin, TQ: 235.degree. C.)
(hereinafter referred to as polymer S).
CF.sub.2.dbd.CF--O--CF.sub.2CF(CF.sub.3)--O--CF.sub.2CF.sub.2--SO.sub.2F
(4-1).
[0226] The polymer C and the polymer S were molded by a
co-extrusion method to obtain a film A of a two layer structure
with a layer (C') (thickness: 12 .mu.m) made of the polymer C and a
layer (S') (thickness: 68 .mu.m) made of the polymer S.
[0227] Further, the polymer S was molded by a melt extrusion method
to obtain a film B comprising a layer (S') (thickness: 30
.mu.m).
[0228] A PTFE film was rapidly stretched and then slit to a
thickness of 100 denier to obtain a monofilament, which was twisted
2,000 times/m to obtain a PTFE yarn, which was used as a
reinforcing yarn. A PET yarn made of a monofilament of 7 denier,
was used as a sacrificial yarn. Plain weaving was conducted so that
one reinforcing yarn and 10 sacrificial yarns would be alternately
arranged, to obtain a reinforcing fabric (density of reinforcing
yarns: 27 yarns/inch, density of sacrificial yarns: 270
yarns/inch).
[0229] The film B, the reinforcing fabric, the film A and a release
PET film (thickness: 100 .mu.m) were overlaid in this order so that
the layer (C') of the film A was located on the release PET film
side, and laminated by using a roll. The release PET film was
peeled off to obtain a reinforcing precursor membrane.
[0230] A paste comprising 29.0 mass % of zirconium oxide (average
particle diameter: 1 .mu.m), 1.3 mass % of methyl cellulose, 4.6
mass % of cyclohexanol, 1.5 mass % of cyclohexane and 63.6 mass %
of water, was transferred by a roll press on the layer (S') side of
the reinforcing precursor membrane, to form a gas-releasing coating
layer. The attached amount of zirconium oxide was 20 g/m.sup.2.
[0231] The reinforcing precursor film having the gas-releasing
coating layer formed on one side, was immersed in an aqueous
solution containing 5 mass % of dimethyl sulfoxide and 30 mass % of
potassium hydroxide at 95.degree. C. for 8 minutes. Thus,
--COOCH.sub.3 of the polymer C and --SO.sub.2F of the polymer S
were hydrolyzed and converted to ion exchange groups, to obtain a
membrane having the layer (C') as the layer (C) and the layer (S')
as the layer (S).
[0232] In an ethanol solution containing 2.5 mass % of an acid-form
polymer of polymer S, zirconium oxide (average particle diameter: 1
.mu.m) was dispersed at a concentration of 13 mass %, to prepare a
dispersion. The dispersion was sprayed on the layer (C) side of the
membrane, to form a gas releasing coating layer, to obtain an ion
exchange membrane having gas releasing coating layers formed on
both surfaces. The attached amount of zirconium oxide was 3
g/m.sup.2.
[Ex. 2]
[0233] An ion exchange membrane was obtained in the same manner as
in Ex. 1, except that as the sacrificial yarn, a PET yarn made of a
monofilament of 7 denier was used and plain weaving was conducted
so that one reinforcing yarn and 12 sacrificial yarns would be
alternately arranged, to obtain a reinforcing fabric (density of
sacrificial yarns: 324 yarns/inch).
[Ex. 3]
[0234] An ion exchange membrane was obtained in the same manner as
in Ex. 1, except that as the sacrificial yarn, a PET yarn made of a
monofilament of 9 denier was used and plain weaving was conducted
so that one reinforcing yarn and four sacrificial yarns would be
alternately arranged, to obtain a reinforcing fabric (density of
sacrificial yarns: 108 yarns/inch).
[Ex. 4]
[0235] A PTFE film was rapidly stretched and then slit to a
thickness of 100 denier to obtain a monofilament, which was twisted
450 times/m to obtain a PTFE yarn, which was used as a reinforcing
yarn. As the sacrificial yarn, a PET yarn made of a monofilament of
12 denier was used. Plain weaving was conducted so that one
reinforcing yarn and eight sacrificial yarns would be alternately
arranged, to obtain a reinforcing fabric (density of reinforcing
yarns: 20 yarns/inch, density of sacrificial yarns: 160
yarns/inch). Other than these, an ion exchange membrane was
obtained in the same manner as in Ex. 1.
[Ex. 5]
[0236] A PTFE film was rapidly stretched and then slit to a
thickness of 100 denier to obtain a monofilament, which was twisted
450 times/m to obtain a PTFE yarn, which was used as a reinforcing
yarn. As the sacrificial yarn, a PET yarn made of a monofilament of
12 denier was used. Plain weaving was conducted so that one
reinforcing yarn and 10 sacrificial yarns would be alternately
arranged, to obtain a reinforcing fabric (density of reinforcing
yarns: 20 yarns/inch, density of sacrificial yarns: 200
yarns/inch). Other than these, an ion exchange membrane was
obtained in the same manner as in Ex. 1.
[Ex. 6]
[0237] A PTFE film was rapidly stretched and then slit to a
thickness of 100 denier to obtain a monofilament, which was twisted
450 times/m to obtain a PTFE yarn, which was used as a reinforcing
yarn. As the sacrificial yarn, a PET yarn made of a monofilament of
5 denier was used. Plain weaving was conducted so that one
reinforcing yarn and 10 sacrificial yarns would be alternately
arranged, to obtain a reinforcing fabric (density of reinforcing
yarns: 20 yarns/inch, density of sacrificial yarns: 200
yarns/inch). Other than these, an ion exchange membrane was
obtained in the same manner as in Ex. 1.
[Ex. 7]
[0238] A PTFE film was rapidly stretched and then slit to a
thickness of 100 denier to obtain a monofilament, which was twisted
450 times/m to obtain a PTFE yarn, which was used as a reinforcing
yarn. As the sacrificial yarn, a PET yarn made of a multifilament
of 3.3 denier was used. Plain weaving was conducted so that one
reinforcing yarn and 10 sacrificial yarns would be alternately
arranged, to obtain a reinforcing fabric (density of reinforcing
yarns: 20 yarns/inch, density of sacrificial yarns: 200
yarns/inch). Other than these, an ion exchange membrane was
obtained in the same manner as in Ex. 1.
[Ex. 8]
[0239] A PTFE film was rapidly stretched and then slit to a
thickness of 100 denier to obtain a monofilament, which was twisted
450 times/m to obtain a PTFE yarn, which was used as a reinforcing
yarn. As the sacrificial yarn, a PET yarn made of a monofilament of
12 denier was used. Plain weaving was conducted so that one
reinforcing yarn and 10 sacrificial yarns would be alternately
arranged, to obtain a reinforcing fabric (density of reinforcing
yarns: 17 yarns/inch, density of sacrificial yarns: 170
yarns/inch). Other than these, an ion exchange membrane was
obtained in the same manner as in Ex. 1.
[0240] The results of measurements of the average distances (d1),
(d2) and (d3), the total area (S), the width of reinforcing yarn,
and the electrolysis voltage, of the ion exchange membrane in each
Ex., are shown in Table 1.
TABLE-US-00001 TABLE 1 Unit Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex.
7 Ex. 8 Rein- Fineness Denier 100 100 100 100 100 100 100 100
forcing Filament Number 1 1 1 1 1 1 1 1 yarn Density of Number/ 27
27 27 20 20 20 20 17 yarns inch Sacri- Fineness Denier 7 7 9 12 12
5 20 12 ficial Filament Number 1 1 1 1 1 1 6 1 yarn Density of
Number/ 270 324 108 160 200 200 200 170 yarns inch Weaving --
Possible Possible Possible Possible Possible Not Possible Possible
(possible/not possible) possible MD d1 .mu.m 908 976 853 1150 1125
-- 1250 1450 cross S .mu.m.sup.2 651 620 726 980 999 -- 1900 950
section n Number 10 12 4 8 10 -- 10 10 d2 .mu.m 70 68 147 120 86 --
93 110 d2/d1 .times. (n + 1) -- 0.85 0.91 0.86 0.94 0.84 -- 0.82
0.83 d3 .mu.m 139 114 206 155 176 -- 207 230 d3/d1 .times. (n + 1)
-- 1.68 1.52 1.21 1.21 1.72 -- 1.82 1.74 Width of rein- .mu.m 128
129 110 145 147 -- 148 143 forcing yarn TD d1 .mu.m 910 929 850
1152 1135 -- 1220 1480 cross S .mu.m.sup.2 680 590 701 1021 1000 --
1935 900 section n Number 10 12 4 8 10 -- 10 10 d2 .mu.m 70 66 140
115 88 -- 98 108 d2/d1 .times. (n + 1) -- 0.85 0.92 0.82 0.90 0.85
-- 0.88 0.80 d3 .mu.m 140 115 215 174 172 -- 169 254 D3/d1 .times.
(n + 1) -- 1.69 1.61 1.26 1.36 1.66 -- 1.52 1.89 Width of .mu.m 125
123 114 152 150 -- 146 142 reinforcing yarn Average d1 .mu.m 909
953 852 1151 1130 -- 1235 1465 of S .mu.m.sup.2 666 605 714 1001
1000 -- 1918 925 MD n Number 10 12 4 8 10 -- 10 10 cross d2 .mu.m
70 67 144 118 87 -- 96 109 section d2/d1 .times. (n + 1) -- 0.85
0.91 0.84 0.92 0.85 -- 0.85 0.82 and d3 .mu.m 140 115 211 164 174
-- 188 242 TD d3/d1 .times. (n + 1) -- 1.69 1.56 1.23 1.28 1.69 --
1.67 1.82 cross Width of .mu.m 127 126 112 149 149 -- 147 143
section reinforcing yarn Aperture ratio % 75 75 75 81 82 -- 81 81
Electrolysis voltage V 3.28 3.26 3.30 3.30 3.27 -- 3.31 3.29
[0241] As shown in Table 1, in Ex. 1 to 2 using ion exchange
membranes wherein the total area (S) was from 500 to 1,200
.mu.m.sup.2 and the number (n) of the elution holes was at least
10, the electrolysis voltage was low as compared with Ex. 3 using
an ion exchange membrane wherein the number (n) of elution holes
was 4.
[0242] In Ex. 5 in which the number (n) of the elution holes was
10, the electrolysis voltage was low as compared with Ex. 4 in
which the number (n) of elution holes was 8.
[0243] In Ex. 6 in which the total area (S) was less than 500
.mu.m.sup.2, the sacrifice yarns were broken in weaving, and the
reinforcing fabric could not be weaved.
[0244] In Ex. 7 in which the total area (S) was more than 1,200
.mu.m.sup.2, the electrolysis voltage was high as compared with Ex.
5 in which the number (n) of elution holes was the same as those of
Ex. 7. Further, the electrolysis voltage was high as compared with
Ex. 4 in which the number (n) of elution holes was 8.
[0245] In Ex. 8 using ion exchange membranes wherein the total area
(S) was from 500 to 1,200 .mu.m.sup.2 and the number (n) of the
elution holes was 10, the electrolysis voltage was low as compared
with Ex. 4 wherein the number (n) of elution holes was 8. Moreover,
in Ex. 8, the electrolysis voltage was high and the effect was
small as compared with Ex. 5 in which the average distance (d1)
from the center of a reinforcing yarn to the center of the adjacent
reinforcing yarn is from 750 to 1,500 .mu.m.
INDUSTRIAL APPLICABILITY
[0246] The electrolysis apparatus having the ion exchange membrane
for alkali chloride electrolysis of the present invention is widely
used for production of chloride and sodium hydroxide or potassium
hydroxide by electrolysis of a sodium chloride aqueous solution or
a potassium chloride aqueous solution.
[0247] This application is a continuation of PCT Application No.
PCT/JP2016/056488, filed on Mar. 2, 2016, which is based upon and
claims the benefit of priority from Japanese Patent Application No.
2015-041301 filed on Mar. 3, 2015. The contents of those
applications are incorporated herein by reference in their
entireties.
REFERENCE SYMBOLS
[0248] 1: ion exchange membrane for alkali chloride electrolysis,
10: electrolyte membrane, 12: layer (C), 14: layer (S), 20:
reinforcing material, 22: reinforcing yarn, 24: sacrificial yarn,
26: filament, 28: elution hole, 121: aqueous sodium chloride, 122:
desalted aqueous sodium chloride, 123: aqueous sodium hydroxide
solution
* * * * *